PUBLISHED

UNITED STATES COURT OF APPEALS

FOR THE FOURTH CIRCUIT

No. 19-1730

In re: SEARCH WARRANT ISSUED JUNE 13, 2019

____________________________

UNITED STATES OF AMERICA,

Plaintiff - Appellee,

v.

UNDER SEAL,

Defendant - Appellant.

Appeal from the United States District Court for the District of Maryland, at Baltimore. 

Liam O’Grady, District Judge. (1:19-mj-02155-TCB-1)

Argued: September 10, 2019 Decided: October 31, 2019

Before GREGORY, Chief Judge, and KING and RUSHING, Circuit Judges.

Reversed and remanded by published opinion. Judge King wrote the opinion, in which

Chief Judge Gregory and Judge Rushing joined. Judge Rushing wrote a separate 

concurring opinion.

ARGUED: James Patrick Ulwick, KRAMON & GRAHAM, P.A., Baltimore, Maryland, 

for Appellant. Derek Edward Hines, OFFICE OF THE UNITED STATES ATTORNEY, 

Baltimore, Maryland, for Appellee. ON BRIEF: Steven M. Klepper, Louis P. Malick, 

KRAMON & GRAHAM, P.A., Baltimore, Maryland, for Appellant. Robert K. Hur, 

United States Attorney, Aaron S.J. Zelinsky, Assistant United States Attorney, OFFICE 

OF THE UNITED STATES ATTORNEY, Baltimore, Maryland, for Appellee.
2

KING, Circuit Judge:

The appellant in these proceedings is a Baltimore law firm (the “Law Firm”) that

challenges the government’s use of a so-called “Filter Team” — created ex parte by a 

magistrate judge in the District of Maryland and comprised of federal agents and 

prosecutors — to inspect privileged attorney-client materials. Those materials were seized

from the Law Firm in June 2019 during the execution of a search warrant issued by the

magistrate judge. The Law Firm requested that the district court enjoin the Filter Team’s

review of the seized materials, invoking the attorney-client privilege and the work-product 

doctrine. When the court denied its request, the Law Firm pursued this appeal. As 

explained below, we are satisfied that use of the Filter Team is improper for several 

reasons, including that, inter alia, the Team’s creation inappropriately assigned judicial 

functions to the executive branch, the Team was approved in ex parte proceedings prior to 

the search and seizures, and the use of the Team contravenes foundational principles that 

protect attorney-client relationships. We therefore reverse and remand.

I.

A.

1.

For about three years, “Lawyer A,” a partner of the Law Firm, handled the 

representation of “Client A” in an investigation conducted by federal authorities in
3

Maryland.

1

 Client A — who is also a Maryland lawyer — was suspected of assisting drug 

dealers in illicit activities, including money laundering and obstruction of federal

investigations. According to the government, its investigation of Client A was obstructed 

by Lawyer A, and the relationship between Lawyer A and Client A triggered an application 

of the crime-fraud exception to the attorney-client privilege and work-product doctrine. In 

light of Lawyer A’s suspected misconduct, the government also initiated an investigation 

of Lawyer A.

As part of those investigative efforts, an IRS agent applied for a warrant to conduct 

a search of the Law Firm’s Baltimore offices. On June 13, 2019, the magistrate judge 

approved the search warrant application and issued the warrant as requested. Based on her 

review of the supporting affidavit of the IRS agent, the judge found probable cause for the

search of the Law Firm and the seizures of client-related materials concerning Lawyer A’s 

representation of Client A.

2.

Contemporaneously with issuance of the search warrant, the magistrate judge

authorized the Filter Team, which had been proposed to the judge ex parte by the 

prosecutors in connection with the search warrant application. In so doing, the judge 

adopted the “Filter Team Practices and Procedures” specified in an attachment to the search

 1 In seeking to protect the identities of those involved in these proceedings, we use 

the nonspecific terms “Law Firm,” “Lawyer A,” and “Client A.” Our use of those terms is 

generally consistent with the record on appeal.
4

warrant application and affidavit (the “Filter Protocol”). See S.J.A. 41-45.2

 The Filter 

Protocol defined the membership of the Filter Team and established the process for its 

review of the materials to be thereafter seized from the Law Firm. Members of the Filter 

Team included lawyers from the United States Attorney’s Office in Maryland’s Greenbelt

Division (the “Filter Team AUSAs”); a legal assistant and a paralegal who also worked

there; agents of the IRS and DEA; and forensic examiners. The Filter Team operated in 

one of the two offices of Maryland’s United States Attorney — the Greenbelt office. 

Pursuant to the Filter Protocol, the Filter Team members were not involved in the 

investigations of Lawyer A and Client A (apart from being Filter Team members). The 

agents and prosecutors conducting the investigations of Lawyer A and Client A (the 

“Prosecution Team”) were excluded from the Filter Team. In contrast to the Filter Team

AUSAs who were assigned to the Greenbelt office, the Prosecution Team lawyers were 

assigned to the United States Attorney’s Baltimore office.

As for the Filter Team’s process of reviewing attorney-client materials seized from 

the Law Firm, the Filter Protocol provided for privilege issues to be handled thusly:

• After seizing materials from the Law Firm, the Filter Team would 

identify and separate privileged and potentially privileged materials

from materials that were not privileged. Under the Filter Protocol, 

privileged materials included “attorney-client information, attorney 

work product information, and client confidences that have not been 

waived,” see S.J.A. 43, 45;

 2 Citations herein to “S.J.A. __” refer to the contents of the Sealed Joint Appendix 

filed by the parties in this appeal. The government later sought to supplement the Sealed 

Joint Appendix by filing an ex parte appendix, the contents of which would be available 

only to itself and the Court and were never available to the Law Firm. On September 12, 

2019, we rejected the filing of the ex parte supplemental appendix.
5

• When seized materials were found by the Filter Team to be 

nonprivileged, the Filter Team AUSAs could forward such materials

directly to the Prosecution Team, without the consent of the Law Firm 

or a court order (the “Privilege Assessment Provision”);

• For privileged and potentially privileged materials, the Filter Team

would decide whether any such seized materials were “responsive to 

the search warrant,” id. at 44;

• For privileged and potentially privileged materials that were

“responsive to the search warrant,” id., the Filter Team AUSAs would 

place them in one of three categories: 

1. Seized materials that were privileged and could not

be redacted; 

2. Seized materials that were privileged but could be 

redacted; or

3. Seized materials that were potentially privileged (for 

example, when the Filter Team identified some

possible exception, such as the crime-fraud 

exception, to a claim of privilege);

• After providing copies to counsel for Lawyer A of the seized materials 

identified as within categories 2 and 3, the Filter Team AUSAs would 

seek an agreement with counsel for Lawyer A concerning whether 

those materials could be forwarded to the Prosecution Team; and

 

• If the Filter Team AUSAs and counsel for Lawyer A disagreed on the 

handling of seized materials, the Filter Team AUSAs would submit

such “items to the court for [a] determination regarding privilege 

and/or proposed redactions of the privileged material,” id.

The Filter Protocol also authorized the Filter Team to provide the Prosecution Team

with seized materials if a Filter Team member “obtain[ed] [a] waiver[] of the attorneyclient privilege” by directly contacting the Law Firm client holding the privilege. See

S.J.A. 42. Under the Protocol, “[i]f a client waive[d] the attorney-client privilege as to 
6

files, no further filter review of [those] files. . . for attorney-client privileged material [was]

required.” Id. 

3.

Five days after the magistrate judge issued the search warrant, on June 18, 2019,

fifteen IRS and DEA agents — who were members of the Filter Team — executed the 

warrant by conducting a six-hour search of the Law Firm’s offices. Those agents seized

voluminous materials, including certain “confidential, privileged documents” of the Law 

Firm concerning, inter alia, Lawyer A’s representation of Client A. See S.J.A. 66. For 

example, the agents electronically copied and seized the contents of Lawyer A’s iPhone 

and computer. The electronically seized materials contained all of Lawyer A’s email 

correspondence, including email correspondence related to Client A and numerous other

Law Firm clients.

3

 More specifically, Lawyer A’s seized email inbox contained 

approximately 37,000 emails, of which 62 were from Client A or contained Client A’s 

surname. And Lawyer A’s seized email “sent items” folder contained approximately

 3 The inventory for the return of the search warrant that was filed under seal in the 

district court describes in very general terms the items seized. See Fed. R. Crim. P. 

41(f)(1)(B) (requiring officer present during execution of warrant to prepare and verify 

inventory of property seized). For example, the inventory states that agents performed 

“extraction[s]” of Lawyer A’s iPhone, of an iPad belonging to the Law Firm, and of a 

laptop belonging to a Firm associate. See S.J.A. 21. The inventory also describes the 

seizures of, inter alia, a laptop, a hard drive, a portable drive, and several compact discs. 

Additionally, the inventory describes the seizures of various physical documents, including 

“handwritten notes” found at the desk of a Law Firm associate, “client notes” found at the 

desk of Lawyer A’s assistant, and a redweld folder containing “communications 

handwritten and typed” found in Lawyer A’s office. Id. at 22-23.
7

15,000 emails, of which 54 had been sent to Client A or contained Client A’s surname. Id.

at 80.4

 An “extensive” portion of the seized emails were “from other [Law Firm] attorneys 

concerning . . . other attorneys’ clients that have no connection with th[e] investigation[s]” 

of Lawyer A and Client A. Id. at 66. Notably, some of those Law Firm clients “are being 

investigated by, or are being prosecuted by, the United States Attorney’s Office [for the 

District of Maryland] for unrelated crimes.” Id.5

During the execution of the search warrant by the IRS and DEA on June 18, 2019,

various Law Firm partners voiced objections, including to the breadth of the search and 

seizures. Those objections were made directly to the federal agents conducting the search,

and were also made to at least two prosecutors, including a member of the Prosecution 

Team. A Law Firm partner specifically requested that the government’s forensic

 4 Our foregoing explanation of the seizures of Lawyer A’s emails is derived in part 

from the affidavit of an information technology professional filed by the Law Firm in the 

district court. See S.J.A. 80-81 (affidavit stating that “I electronically reviewed [Lawyer 

A’s] email folders on the [F]irm’s computer server and determined that (a) [Lawyer A’s] 

email inbox contained a total of 37,114 emails with a total size of 9,124,544 KB, of which 

only 62 emails with a total size of 21,582 KB were from [Client A] or contained [Client 

A’s surname]; and (b) [Lawyer A’s] email sent items contained 15,219 emails with a total 

size of 2,308,938 KB, of which only 54 emails with a total size of 20,049 KB were sent to 

[Client A] or contained [Client A’s surname]”). No evidence contradicting that affidavit 

was presented to the district court.

5 In addition to the seizures by federal agents of thousands of emails and other

communications between Lawyer A and persons other than Client A, the IRS and DEA 

agents seized multiple compact discs containing electronic documents that Lawyer A had 

received from lawyers who had previously represented Client A.
8

examiners limit their seizures of Lawyer A’s emails to those that included Client A’s name

or other relevant search terms. Those requests were all rejected.

6

By letter delivered to the United States Attorney on June 21, 2019, the Law Firm

asserted that the search and seizures contravened the Constitution, Federal Rules of 

Criminal Procedure, and United States Attorneys’ Manual. Additionally, the Law Firm 

advised the government that the Firm had a duty “to preserve client confidences and 

secrets,” see S.J.A. 71, and that it was “ethically mandated to urge the return of all items 

seized by the government,” id. at 72. The Law Firm’s letter objected to the use of the Filter 

Team and requested that the government return the seized materials so that the Firm could 

conduct a privilege review — which would have been the process had the government used

subpoenaes duces tecum rather than a search warrant. The Law Firm also requested that

the government not examine any of the seized materials until the Firm had an opportunity

to complete its privilege review. Alternatively, the Law Firm asked the government to

immediately submit the seized materials to the magistrate judge or the district court for in 

camera inspection. The government never responded to the Law Firm’s letter.

 6 The facts specified herein with respect to the Law Firm’s objections to the 

execution of the search warrant, and the government’s refusal to limit the seizures of 

Lawyer A’s emails, are spelled out in the affidavit of a Law Firm partner that was filed in 

the district court. See S.J.A. 67 (affidavit stating that “[o]n June 18, 2019, my law partners 

and I immediately voiced [the Law Firm’s] objections to the search and seizure, both to 

agents conducting the search and by phone to Assistant United States Attorneys . . . . I 

asked the [g]overnment’s forensic examiners to limit the downloading of [Lawyer A’s] 

emails to those that included [Client A’s surname] or other relevant search terms, but they 

refused to do so without explanation”). The government did not rebut the lawyer’s 

affidavit.
9

B.

On June 26, 2019, Client A — whose own office had also been searched by federal 

agents and whose files were seized — moved in the district court for relief from the Filter 

Protocol, which also applied to that search. The following day, the court ordered that the 

Filter Team not deliver to the Prosecution Team any materials that were seized from Client 

A and the Law Firm, pending further order of the court.7

On June 28, 2019, the Law Firm separately moved in the district court for injunctive 

relief. More specifically, the Law Firm sought a temporary restraining order and a 

preliminary injunction, pursuant to Rule 65 of the Federal Rules of Civil Procedure, and

the return of seized property, pursuant to Rule 41(g) of the Federal Rules of Criminal 

Procedure (collectively, the “Injunction Requests”). On July 1, 2019, the government 

responded to and opposed the Law Firm’s Injunction Requests. The Law Firm replied the 

very next day.

Eight days later, on July 10, 2019, the district court conducted a telephonic hearing 

on the Injunction Requests.

8

 During that hearing, the Law Firm’s counsel explained that 

the Law Firm had more than twenty lawyers, and he described the Firm’s extensive and 

ongoing law practice in Maryland, including its involvement in a vast amount of criminal

 7 Because all the district judges in the District of Maryland recused themselves from 

these proceedings, a district judge in the Eastern District of Virginia was designated to 

handle them. The magistrate judge on this case is also an Eastern District of Virginia judge 

designated for service in the District of Maryland.

8 The district court was not available for an earlier hearing due to the extended 

Fourth of July holiday weekend and the court’s schedule. 
10

and civil litigation and related legal services. Counsel emphasized to the court that Lawyer 

A’s entire email file had been copied and seized by the federal agents and that the file

contained privileged communications with and between various lawyers and clients of the 

Law Firm concerning criminal and civil matters unrelated to the investigations of Lawyer 

A and Client A. Counsel advised the court that the Law Firm had conducted a search of 

Lawyer A’s emails using Client A’s surname and identified only 116 responsive emails in 

the approximately 52,000 emails that were seized from Lawyer A’s email file. The Law 

Firm’s counsel emphasized his objections to any use of a government filter team and 

argued that the Filter Protocol approved by the magistrate judge was fatally flawed. He 

stressed the Filter Protocol’s illegality as to all clients of the Law Firm. Counsel added

that the Filter Team would have access to and would be reviewing seized materials related 

to Law Firm clients that the Filter Team members could be investigating, or might thereby 

become interested in investigating.

The government responded that the Filter Team AUSAs had asked the Law Firm 

for a list of clients with pending matters in the United States Attorney’s Office, in order to 

confirm that no Filter Team member was involved in such matters.

9

 The Law Firm, 

however, declined to provide that information. The government represented that it had no 

alternative but to seize Lawyer A’s entire email file because an onsite review was

impractical. The government also argued that, if it had provided search terms to the Law 

 9 In addition to a list of Law Firm clients with pending matters in the United States 

Attorney’s Office, a Filter Team AUSA requested that a Firm partner supply the Filter 

Team with a list of all Lawyer A’s “cases.” See S.J.A. 74.
11

Firm, those terms would have revealed what the government was searching for, and those 

revelations might have allowed Lawyer A to obstruct its investigations. In addition, the 

government claimed that using search terms might cause the Filter Team to overlook emails 

relevant to the investigations. 

At the conclusion of the telephonic hearing of July 10, 2019, the district court orally 

denied the Law Firm’s Injunction Requests, ruling that the Firm had not shown “any 

likelihood of irreparable harm.” See S.J.A. 122. The court related that “filter teams can be 

neutral,” and that this Filter Team was “operating under the [c]ourt’s direction.” Id. at 120. 

The court observed that, “absent a finding that there has been some breach of [the 

prosecutors’] ethical responsibilities and duties in this case, which rarely occurs,” the Filter 

Protocol was not “inappropriate.” Id. at 121. Additionally, the court related that “having 

an independent group” of prosecutors review the seized materials did not “create[] great 

risk or create[] the appearance of unfairness.” Id. The court said there was no “per se rule 

that law firms are to be treated so differently that neutral examiners must be appointed in 

every case.” Id. Finally, the court remarked that the Law Firm had “delay[ed] in coming 

to the [c]ourt,” and stated that the Filter Team had made substantial progress in reviewing 

the seized materials. Id. at 122.

On July 11, 2019 — the day after the hearing — the district court entered an order

denying the Injunction Requests because the Law Firm had not established that it would 

suffer irreparable harm absent injunctive relief. See In re Search of Under Seal, No. 1:19-

mj-02155 (D. Md. July 11, 2019), ECF No. 11 (the “Denial Order”). The Denial Order

stated, in part:
12

In reviewing the search warrant, the [m]agistrate [j]udge knew that the search 

was to be of [a] law firm[] and imposed appropriate and well-established 

constraints on the [Filter Team] that would be reviewing the seized 

documents. There is no inherent conflict in having the seized documents 

reviewed by [the Filter Team] composed of Assistant United States 

Attorneys who have no connection to the underlying case or [the Law Firm] 

and no contact with the [Prosecution Team] on this case. . . . As a result, the 

[c]ourt finds that the limits in the search warrant and the constraints imposed 

on the [Filter Team] are such that the appointment of a special master or 

magistrate judge is not necessary to protect [the Law Firm] or its clients from 

irreparable harm.

Id. at 2. 

Later that day, the Law Firm noted this appeal, pursuant to 28 U.S.C. § 1292(a)(1). 

That jurisdictional provision authorizes appellate review of a district court’s decision 

denying injunctive relief. 

On July 17, 2019, after the Law Firm’s appeal was lodged, the district court entered 

an agreed order modifying the Privilege Assessment Provision of the Filter Protocol. 

Specifically, the court altered that Provision to require that the Filter Team’s forwarding of 

seized materials to the Prosecution Team be first approved by the Law Firm or by the court

(the “Modified Privilege Assessment Provision”). Prior to that modification, the Privilege 

Assessment Provision authorized the Filter Team to deem seized materials nonprivileged

and give them directly to the Prosecution Team.

C.

On July 12, 2019, the Law Firm moved in this Court for an injunction pending 

appeal. Five days thereafter, on July 17, 2019, we granted the Law Firm some relief,

directing the government to “cease review of the seized files and forthwith place the files 
13

in the custody of the [m]agistrate [j]udge to be held under seal pending further order of this 

Court.” See ECF No. 39.10 

After expediting this appeal and receiving the Law Firm’s opening brief, we directed 

the government to specifically address four issues in its brief. Especially pertinent here, 

we requested that the government address whether judicial functions had been improperly 

assigned to the Filter Team.

We conducted oral argument in Richmond on September 10, 2019. Two days later, 

on September 12, 2019, we entered an order that reversed “the district court’s denial of the 

Law Firm’s request that review of the seized materials be made by the magistrate judge, 

rather than by the Filter Team.” See ECF No. 72 (the “Interim Order”). Our Interim Order

reassigned the Filter Team’s duties and functions to the magistrate judge and gave guidance 

in that regard. More specifically, we advised the magistrate judge to review all seized 

materials, identify those not related to Client A and return them to the Law Firm, and 

conduct a privilege evaluation of the remaining materials. As promised in the Interim 

Order, we now issue this opinion to explain our rulings in these proceedings.

11

 10 On July 22, 2019, the government filed with our Court a “Notice of Compliance” 

with our directive of July 17, 2019, explaining that the Filter Team had provided the 

magistrate judge with all files — both paper and electronic — seized from the Law Firm. 

See ECF No. 44. By July 22, 2019, the seized materials had been “substantially reviewed 

and coded by the Filter Team.” Id. As of that date, the government had not returned any 

of the seized materials to the Law Firm.

11 The government represented at oral argument that it had given the magistrate 

judge all the Filter Team’s work product that related to the seized materials. And the 

lawyer asserted that the government’s July 22, 2019 Notice of Compliance so stated. We

are not at all certain, however, that the Notice provides such advice. As will be explained, 

(Continued)
14

II.

The Supreme Court has described the award of a preliminary injunction as “an 

extraordinary remedy [that is] never awarded as of right.” See Winter v. Nat. Res. Defense 

Council, Inc., 555 U.S. 7, 24 (2008). To prevail on a request for such preliminary relief, 

the plaintiff must establish that (1) it is likely to succeed on the merits, (2) it is likely to 

suffer irreparable harm absent the requested preliminary relief, (3) the balance of the 

equities weighs in its favor, and (4) a preliminary injunction is in the public interest. See 

Centro Tepeyac v. Montgomery Cty., 722 F.3d 184, 188 (4th Cir. 2013) (en banc).

When a district court denies a preliminary injunction based on its evaluation of only

one of the foregoing factors, we review its assessment of that factor for abuse of discretion. 

See Fusaro v. Cogan, 930 F.3d 241, 248 (4th Cir. 2019) (explaining abuse of discretion 

standard); cf. Henderson ex rel. NLRB v. Bluefield Hosp. Co., 902 F.3d 432, 439 (4th Cir. 

2018) (recognizing that court can deny preliminary injunction when party fails to satisfy 

any one of four factors). In that circumstance, however, we must perform our own 

assessment of the factors not addressed by the district court. See Hobby Lobby Stores, Inc. 

v. Sebelius, 723 F.3d 1114, 1145 & n.21 (10th Cir. 2013) (en banc). We then evaluate the

 

because the Filter Team was performing judicial functions when conducting its review 

pursuant to the Privilege Assessment Provision and the Modified Privilege Assessment 

Provision, the government is obliged to fully advise the magistrate judge as to the work 

that was performed by the Filter Team and to deliver any Filter Team work product to the 

judge. See Interim Order 2 (“All work product of the Filter Team shall forthwith be 

delivered by the [g]overnment to the magistrate judge for filing under seal.”).
15

court’s “ultimate decision” to deny injunctive relief for abuse of discretion. See Gonzales 

v. O Centro Espirita Beneficente Uniao do Vegetal, 546 U.S. 418, 428 (2006).

In performing an abuse of discretion review, we assess the district court’s factual 

findings for clear error and its legal conclusions de novo. See Fusaro, 930 F.3d at 248. A

court abuses its discretion in denying preliminary injunctive relief when it “rest[s] its 

decision on a clearly erroneous finding of a material fact, or misapprehend[s] the law with 

respect to underlying issues in litigation.” See Centro Tepeyac, 722 F.3d at 188 (internal 

quotation marks omitted). Furthermore, a court “abuses its discretion when it makes an 

error of law,” see Koon v. United States, 518 U.S. 81, 100 (1996), or when it ignores 

“unrebutted, legally significant evidence,” see Alvarez Lagos v. Barr, 927 F.3d 236, 255 

(4th Cir. 2019).

III.

In making our assessment of the various injunction issues, we begin with whether 

the Law Firm is likely to suffer irreparable harm absent injunctive relief. We proceed in 

this manner because the district court’s denial of the Law Firm’s Injunction Requests was 

predicated solely on the irreparable harm factor of the four-part preliminary injunction test. 

We then evaluate the other factors, which the district court did not reach and address. More 

specifically, we consider and decide whether the Law Firm has demonstrated a likelihood 

of success on the merits of its challenge to the Filter Team and its Protocol, whether the 

balance of the equities weighs in the Firm’s favor, and whether an award of injunctive relief 
16

is in the public interest. See Centro Tepeyac v. Montgomery Cty., 722 F.3d 184, 188 (4th 

Cir. 2013) (en banc).12

A.

With respect to the irreparable harm factor, the Law Firm is obliged to demonstrate 

that it is likely to suffer such harm in the absence of injunctive relief. See Winter v. Nat. 

Res. Defense Council, Inc., 555 U.S. 7, 20 (2008). The Law Firm maintains that, absent

relief from the Filter Team and its Protocol, federal agents and prosecutors on the Filter 

Team will continue their review of “tens of thousands” of privileged materials concerning

Law Firm clients other than Client A. See Br. of Appellant 45. The Law Firm emphasizes

(1) that 99.8 percent of the 52,000 emails seized by the government were not from Client 

A, were not sent to Client A, and did not mention Client A’s surname; and (2) that many 

of those emails contained privileged information relating to other clients of the Firm, 

including clients who are potential subjects or targets of government investigations.

13

1.

In ruling that the Law Firm did not satisfy the irreparable harm factor, the district 

court failed to address the Law Firm’s unrebutted evidence with respect to Lawyer A’s 

 12 Although the district court mentioned the balance of the equities factor during the 

telephonic hearing of July 10, 2019, the court did not rely on that factor to deny the 

Injunction Requests.

13 Although the government argues on appeal that the Law Firm’s evidence is not 

accurate and cannot be relied on, it failed to present any contradictory evidence to the 

district court. See United States v. Anderson, 481 F.2d 685, 702 n.19 (4th Cir. 1973) 

(emphasizing importance of building appellate record in district court).
17

emails. See Alvarez Lagos v. Barr, 927 F.3d 236, 255 (4th Cir. 2019) (explaining that 

failure to address “unrebutted, legally significant evidence” constitutes abuse of 

discretion). That is, the court ignored evidence that less than one percent of the seized 

emails were from Client A, were to Client A, or mentioned Client A’s surname, and that 

many seized emails contained privileged communications and attorney work product 

concerning other Law Firm clients. Additionally, the court failed to acknowledge the fact

that some of those communications were from or about clients who “are being investigated 

by, or are being prosecuted by,” federal prosecutors. See S.J.A. 66. As a result, the court

did not grapple with the harm that is likely to be inflicted on the Law Firm and its clients 

from the Filter Team’s review of many of the seized emails.

14 The court thus abused its 

discretion in that respect.

2.

 14 During the oral argument in this appeal, the government maintained that the Filter 

Team is entitled to review materials seized from the Law Firm that are not facially relevant 

to Client A. The government’s justification for that proposition is that the Filter Team 

needs “context” for its privilege determinations. See Oral Argument at 43:20, United States 

v. Under Seal, No. 19-1730 (4th Cir. Sept. 10, 2019), http://www.ca4.uscourts.gov/oralargument/listen-to-oral-arguments. According to this “context” argument, the government 

was entitled to seize and review documents for which probable cause was lacking. 

Unsurprisingly, the government has no supporting authority in that regard. See United 

States v. Comprehensive Drug Testing, Inc., 621 F.3d 1162, 1172 (9th Cir. 2010) (en banc) 

(criticizing government “overreach[]” in seizure of electronic data unsupported by 

probable cause), abrogated on other grounds by Hamer v. Neighborhood Hous. Servs. of 

Chi., 138 S. Ct. 13, 16-17 (2017).
18

The district court’s failure to consider the Law Firm’s unrebutted evidence

compounded other errors of law that the court made with respect to the irreparable harm 

factor. See Koon v. United States, 518 U.S. 81, 100 (1996) (explaining that a court “by 

definition abuses its discretion when it makes an error of law”). More specifically, the 

court erred by giving short shrift to the important legal principles that protect attorneyclient relationships, which we are compelled to elucidate herein.

a.

As we know, the attorney-client privilege is “the oldest of the privileges for 

confidential communications known to the common law.” See Upjohn Co. v. United 

States, 449 U.S. 383, 389 (1981); see also In re Grand Jury Subpoenas, 454 F.3d 511, 519 

(6th Cir. 2006) (explaining that “[t]he privilege protecting confidential communications 

between an attorney and his client dates back to the Tudor dynasty”). The attorney-client 

privilege empowers a client — as the privilege holder — “to refuse to disclose and to 

prevent any other person from disclosing confidential communications between him and 

his attorney.” See Black’s Law Dictionary 129 (6th ed. 1990). And in proceedings such 

as these, lawyers are obliged to protect the attorney-client privilege to the maximum 

possible extent on behalf of their clients. See Republic Gear Co. v. Borg-Warner Corp., 

381 F.2d 551, 556 (2d Cir. 1967) (recognizing that lawyer has duty to invoke claim of 

privilege on client’s behalf); Model Rules of Prof’l Conduct r. 1.6(a), (c) (Am. Bar Ass’n 

1983) (explaining that lawyer owes duty of confidentiality to client and must prevent 

unauthorized disclosure of confidential information). That proposition underlies the Law 

Firm’s uncontested standing to pursue the legal positions it advances in this appeal. See 
19

Fisher v. United States, 425 U.S. 391, 402 n.8 (1976) (“[I]t is universally accepted that the 

attorney-client privilege may be raised by the attorney[.]”); In re Grand Jury Proceedings, 

727 F.2d 1352, 1354-55 (4th Cir. 1984) (emphasizing that a lawyer “is entitled to raise [a 

claim of] privilege on behalf of his . . . client”).

The purpose of the attorney-client privilege is to ensure “full and frank 

communication” between a client and his lawyer and “thereby promote broader public

interests in the observance of law and administration of justice.” See Upjohn Co., 449 U.S. 

at 389. As the Supreme Court has consistently emphasized, the attorney-client privilege 

exists because “sound legal advice or advocacy serves public ends and . . . such advice or 

advocacy depends upon the lawyer’s being fully informed by the client.” Id.; see also Hunt 

v. Blackburn, 128 U.S. 464, 470 (1888) (“The rule which places the seal of secrecy upon 

communications between client and attorney is founded upon the necessity, in the interest 

and administration of justice, of the aid of persons having knowledge of the law and skilled 

in its practice, which assistance can only be safely and readily availed of when free from 

the consequences or the apprehension of disclosure.”).

Although the work-product doctrine does not trace as far into history as the attorneyclient privilege, it is no less important. The Supreme Court explicitly recognized and 

explained the work-product doctrine more than seventy years ago in its seminal decision 

in Hickman v. Taylor. See 329 U.S. 495, 510-11 (1947). In Hickman, the Court 

underscored that a lawyer must be able to “work with a certain degree of privacy, free from 

unnecessary intrusion by opposing parties and their counsel.” Id. at 510. Elaborating on 

that principle, the Court emphasized that “[p]roper preparation of a client’s case demands 
20

that [a lawyer] assemble information, sift what he considers to be the relevant from the 

irrelevant facts, prepare his legal theories and plan his strategy without undue and needless 

interference.” Id. at 511. As the Court warned, absent strong protection for work product, 

“[i]nefficiency, unfairness and sharp practices would inevitably develop in the giving of 

legal advice and in the preparation of cases for trial,” all to the detriment of clients and “the 

cause of justice.” Id. 

Thus, the Supreme Court has explicitly approved what it called “a qualified 

privilege,” to be held by lawyer and client alike, “for certain materials prepared by an 

attorney ‘acting for his client in anticipation of litigation.’” See United States v. Nobles, 

422 U.S. 225, 237-38 (1975) (quoting Hickman, 329 U.S. at 508). That privilege is the 

work-product doctrine, which has now been incorporated into the Federal Rules of Civil 

Procedure, see Fed. R. Civ. P. 26(b)(3), and the Federal Rules of Criminal Procedure, see 

Fed. R. Crim. P. 16(a)(2), (b)(2).

There are two types of attorney work product that are within the ambit of the 

doctrine: (1) fact work product, which is “a transaction of the factual events involved,” 

and (2) opinion work product, which “represents the actual thoughts and impressions of 

the attorney.” See In re Grand Jury Subpoena, 870 F.3d 312, 316 (4th Cir. 2017) (internal 

quotation marks omitted). Opinion work product, we have recognized, “enjoys a nearly 

absolute immunity” and can be discovered by adverse parties “only in very rare and 

extraordinary circumstances.” Id. (internal quotation marks omitted). Fact work product

is somewhat less protected, and discovery thereof by others may only be had in limited 

circumstances, where a party shows “both a substantial need and an inability to secure the 
21

substantial equivalent of the materials by alternate means without undue hardship.” Id.

(internal quotation marks omitted).

Notably, the attorney-client privilege and the work-product doctrine jointly support 

the Sixth Amendment’s guarantee of effective assistance of counsel. See U.S. Const. 

amend. VI (“In all criminal prosecutions, the accused shall enjoy the right . . . to have the 

Assistance of Counsel for his defence.”); Strickland v. Washington, 466 U.S. 668, 686 

(1984) (analyzing Sixth Amendment right to effective assistance of counsel). For example, 

in assessing the interplay between the attorney-client privilege and the Sixth Amendment, 

we have emphasized that “[t]he essence of the Sixth Amendment right to effective 

assistance of counsel is, indeed, privacy of communication with counsel.” See United 

States v. Brugman, 655 F.2d 540, 546 (4th Cir. 1981); cf. DeMassa v. Nunez, 770 F.2d 

1505, 1507 (9th Cir. 1985) (describing Sixth Amendment as a “source” for the expectation 

of privacy in attorney-client communications); 1 Geoffrey C. Hazard, Jr. et al., The Law of 

Lawyering § 10.14, 10-91 (4th ed. Supp. 2019) (explaining that “[t]he attorney-client 

privilege has ties to the Sixth Amendment”). Absent privacy of communications and the 

“full and frank” discussions that flow therefrom, a lawyer could be deprived of the 

information necessary to prepare and present his client’s defense. See Upjohn Co., 449 

U.S. at 389. 

Similarly, the work-product doctrine fulfills an essential and important role in 

ensuring the Sixth Amendment right to effective assistance of counsel. The Supreme Court 

has recognized that the work-product doctrine is vital to “assur[e] the proper functioning 

of the criminal justice system,” in that it “provid[es] a privileged area within which [a 
22

lawyer] can analyze and prepare his client’s case.” See Nobles, 422 U.S. at 238; see also 

In re Grand Jury Subpoenas, 454 F.3d at 520 (explaining that “people should be free to 

make requests of their attorneys without fear, and that their attorneys should be free to 

conduct research and prepare litigation strategies without fear that these preparations will 

be subject to review by outside parties”). Without that “privileged area,” a lawyer’s ability 

to plan and present his client’s defense will be impaired. See Nobles, 422 U.S. at 238; see 

also Hickman, 329 U.S. at 511.15

b.

In ruling that the Law Firm had not established a likelihood of irreparable harm, the 

district court erred as a matter of law by affording insignificant weight to the foregoing 

principles protecting attorney-client relationships. See Upjohn Co., 449 U.S. at 389 

(emphasizing importance of attorney-client privilege); Nobles, 422 U.S. at 237-38 

(recognizing significance of protecting lawyer work product); cf. Gunnells v. Healthplan 

Servs., Inc., 348 F.3d 417, 434 (4th Cir. 2003) (explaining that court abuses discretion in 

 15 Although the attorney-client privilege and work-product doctrine are essential 

components of our adversarial system, neither is absolute. For example, claims of attorneyclient privilege or work-product protection can sometimes be defeated by the crime-fraud 

exception. See In re Grand Jury Proceedings #5 Empanelled Jan. 28, 2004, 401 F.3d 247, 

251 (4th Cir. 2005). Put succinctly, “[b]oth the attorney-client and work-product privileges 

may be lost . . . when a client gives information to an attorney for the purpose of committing 

or furthering a crime or fraud.” Id. In these proceedings, the government has invoked that 

exception as to Client A of Lawyer A.
23

ignoring applicable legal principles). Crucially, the court failed to recognize that an 

adverse party’s review of privileged materials seriously injures the privilege holder. See 

United States v. Philip Morris Inc., 314 F.3d 612, 622 (D.C. Cir. 2003) (concluding that a 

party had demonstrated the likelihood of irreparable harm predicated on “the general injury 

caused by the breach of the attorney-client privilege and the harm resulting from the 

disclosure of privileged documents to an adverse party”), abrogated on other grounds by

Mohawk Indus., Inc. v. Carpenter, 558 U.S. 100, 103 (2009); In re Perrigo Co., 128 F.3d 

430, 437 (6th Cir. 1997) (explaining that “forced disclosure of privileged material may 

bring about irreparable harm”); Klitzman, Klitzman & Gallagher v. Krut, 744 F.2d 955, 

960-61 (3d Cir. 1984) (ruling that law firm had demonstrated likelihood of irreparable harm 

where government seized thousands of files containing privileged information).

3.

When the pertinent legal principles are properly applied to the unrefuted evidence, 

the Filter Team’s review of the materials seized from the Law Firm was and is injurious to 

the Firm and its clients. And that harm is plainly irreparable, in that the Filter Team’s 

review of those privileged materials cannot be undone. We are therefore satisfied that the 

Law Firm will be irreparably harmed absent an award of injunctive relief against the Filter 

Team and its Protocol.16 

 16 We observe that the Filter Team and its Protocol may inflict other injuries on the 

Law Firm. For example, adverse publicity about the search of the Law Firm, the Filter 

Team, and its Protocol could make potential clients less likely to seek out and retain the 

Firm. Additionally, potential and current clients might be reluctant to candidly 

communicate with the Law Firm attorneys because they fear government review of their 

(Continued)
24

B.

Turning to the injunction factors not reached and addressed by the district court, we 

begin with the likelihood of success factor. In order to prevail on that factor, the Law Firm 

must make a “clear showing” that the Filter Team and its Protocol are legally flawed. See 

Pashby v. Delia, 709 F.3d 307, 321 (4th Cir. 2013). Stated differently, the Law Firm is 

obliged to demonstrate it is likely to succeed on its request that the magistrate judge —

rather than the Filter Team — perform the privilege review of the seized materials. 

In that regard, the Law Firm maintains that the Filter Team and its Protocol are

simply “incompatible with courts’ historical protection of the attorney-client privilege and 

the work-product doctrine.” See Br. of Appellant 35. The Law Firm contends that there is 

a clear appearance of — and potential for — improprieties when government agents are 

authorized to rummage through attorney-client communications, particularly when less 

than one percent of those communications relate to the investigations at issue. And the 

Law Firm posits that use of the Filter Team in these circumstances will chill the free flow 

of information between clients and lawyers. Put simply, the Law Firm maintains that

judicial functions are involved in all aspects of assessing and deciding privilege issues. 

The Law Firm thus argues that a magistrate judge or a special master must perform those 

functions.

 

communications and breaches of confidentiality. Consequently, the Law Firm is likely to

be deprived of information necessary to the proper handling of its cases. See Upjohn Co., 

449 U.S. at 389 (explaining necessity of “full and frank communication” between client 

and his lawyer).
25

As further explained below, we are satisfied that the Law Firm has shown that it is 

likely to succeed on the merits of its challenge to the Filter Team and its Protocol. In 

approving the Filter Team and its Protocol, the magistrate judge made several legal errors 

by, inter alia: (1) assigning judicial functions to the Filter Team; (2) authorizing the Filter 

Team and its Protocol in ex parte proceedings that were conducted prior to the search and 

seizures at the Law Firm; and (3) failing to properly weigh the foundational principles that 

protect attorney-client relationships.

1.

To start, the magistrate judge — by authorizing the Filter Team and its Protocol —

erred in assigning judicial functions to the executive branch. We have recognized that,

when a dispute arises as to whether a lawyer’s communications or a lawyer’s documents 

are protected by the attorney-client privilege or work-product doctrine, the resolution of 

that dispute is a judicial function. See NLRB v. Interbake Foods, LLC, 637 F.3d 492, 498, 

500 (4th Cir. 2011) (concluding that, in deciding whether to enforce an administrative 

subpoena seeking potentially privileged documents, a court “cannot delegate” an in camera

review of documents to an agency, but must itself decide a claim of privilege); see also In 

re The City of New York, 607 F.3d 923, 947 (2d Cir. 2010) (observing that evaluating 

privilege claim is always a judicial function); In re Grand Jury Proceedings #5 Empanelled 

Jan. 28, 2004, 401 F.3d 247, 256 (4th Cir. 2005) (remanding to district court for in camera

review concerning privileged communications and applicability of crime-fraud exception). 

Indeed, the Constitution vests “[t]he judicial Power” solely in the federal courts, see U.S. 

Const. art. III, § 1, which includes “the duty of interpreting and applying” the law, see 
26

Massachusetts v. Mellon, 262 U.S. 447, 488 (1923). Put simply, a court is not entitled to 

delegate its judicial power and related functions to the executive branch, especially when 

the executive branch is an interested party in the pending dispute. See Interbake Foods,

637 F.3d at 501 (affirming refusal “to delegate” to an administrative law judge the 

judiciary’s “responsibility to decide the issue of privilege”); NLRB v. Detroit Newspapers, 

185 F.3d 602, 606 (6th Cir. 1999) (concluding that “district court had the obligation . . . to 

determine whether the subpoenaed documents were protected by some privilege, and had 

no discretion to delegate that duty”).

In these proceedings, the Privilege Assessment Provision of the Filter Protocol

contravened that nondelegation principle. Put succinctly, the Privilege Assessment 

Provision erroneously authorized the executive branch — that is, the Filter Team — to

make decisions on attorney-client privilege and the work-product doctrine. As our good 

colleague Judge Niemeyer recognized in Interbake Foods, a court simply cannot delegate 

its responsibility to decide privilege issues to another government branch. See 637 F.3d at

498, 500-01 (recognizing that court must decide privilege disputes); see also In re The City 

of New York, 607 F.3d at 947 (observing that evaluating privilege claim is a judicial 

function). 

To compound that error, the Privilege Assessment Provision delegated judicial 

functions to non-lawyer members of the Filter Team. In other words, the Privilege 

Assessment Provision authorized paralegals and IRS and DEA agents to designate seized

documents as nonprivileged, and allowed the Filter Team AUSAs to deliver such

documents to the Prosecution Team without the approval of the Law Firm or a court order. 
27

The Third Circuit has strongly criticized a similar protocol and explicitly ruled that nonlawyer federal agents could not make privilege determinations. See In re Search of Elec. 

Commc’ns, 802 F.3d 516, 530 & n.54 (3d Cir. 2015).

In addition to the separation of powers issues that arise from the Filter Protocol’s

delegation of judicial functions to the Filter Team, there are other apparent legal problems

therewith. There is the possibility that a filter team — even if composed entirely of trained

lawyers — will make errors in privilege determinations and in transmitting seized materials 

to an investigation or prosecution team. On this point, the Sixth Circuit recognized several 

years ago that such filter teams present “reasonably foreseeable risks to privilege” and

“have been implicated . . . in leaks of confidential information to prosecutors.” See In re 

Grand Jury Subpoenas, 454 F.3d at 523. As Judge Boggs aptly explained, a filter team

might “have an interest in preserving privilege, but it also possesses a conflicting interest 

in pursuing the investigation, and . . . some [filter] team attorneys will make mistakes or 

violate their ethical obligations. It is thus logical to suppose that [filter] teams pose a 

serious risk to holders of privilege.” Id.

As the Sixth Circuit also emphasized, filter team errors can arise from differences 

of opinion regarding privilege. See In re Grand Jury Subpoenas, 454 F.3d at 523. In 

explaining that problem, the court elaborated that a filter team’s members “might have a 

more restrictive view of privilege” than the subject of the search, given their prosecutorial 

interests in pursuing the underlying investigations. Id. That “more restrictive view of 

privilege” could cause privileged documents to be misclassified and erroneously provided

to an investigation or prosecution team. Id.
28

The Sixth Circuit also acknowledged that filter team errors can result from mistakes 

or neglect, and described one infamous occurrence as follows:

In United States v. Noriega, 764 F. Supp. 1480 (S.D. Fla. 1991), . . . the 

government’s [filter] team missed a document obviously protected by 

attorney-client privilege, by turning over tapes of attorney-client 

conversations to members of the investigating team. This Noriega incident 

points to an obvious flaw in the [filter] team procedure: the government’s 

fox is left in charge of the [law firm’s] henhouse, and may err by neglect or 

malice, as well as by honest differences of opinion.

See In re Grand Jury Subpoenas, 454 F.3d at 523 (emphasis added). 

Strikingly, the risks to attorney-client privilege and the work-product doctrine that 

were identified by the Sixth Circuit have been recently realized in the District of Maryland, 

from which this appeal arises. See United States v. Elbaz, No. 8:18-cr-00157, slip op. at 

4-6 (D. Md. June 20, 2019), ECF No. 216 (the “Elbaz opinion”). According to the Elbaz

opinion, the government’s filter team improperly disclosed thousands of potentially 

privileged documents to a prosecution team, which then examined some of the documents. 

Id. Those blunders occurred nearly a year before this Filter Team was authorized by the 

magistrate judge. Id. at 3-6. And the Elbaz opinion detailing that filter team’s mistakes 

was filed in the District of Maryland on June 20, 2019, just a week after the magistrate 

judge’s authorization of this Filter Team on June 13, 2019, and three weeks before the

district court’s Denial Order of July 11, 2019.

In sum, the Filter Protocol improperly delegated judicial functions to the Filter 

Team. And the magistrate judge failed to recognize and consider the significant problems 

with that delegation, which left the government’s fox in charge of guarding the Law Firm’s 

henhouse. See In re Grand Jury Subpoenas, 454 F.3d at 523.
29

2.

Relatedly, the magistrate judge erred by prematurely authorizing the Filter Team 

and its Protocol in ex parte proceedings that it conducted on June 13, 2019, five days before

the search warrant was executed and voluminous seizures were made from the Law Firm.17 

First, the timing of the judge’s authorization undermined the judge’s ability to exercise 

discretion with respect to the Filter Team and its Protocol, in that the judge could not have 

been fully informed of what was seized from the Law Firm. See James v. Jacobson, 6 F.3d 

233, 238 (4th Cir. 1993) (emphasizing that court’s exercise of discretion must be 

“informed”). And the judge may well have rejected the Filter Team and its Protocol if the 

judge had known (1) that 99.8 percent of the 52,000 seized emails were not from Client A,

were not sent to Client A, and did not mention Client A’s surname; and (2) that many of 

those seized emails contained privileged information concerning other clients of the Law 

Firm. Put simply, the judge should have deferred the decision concerning the proposed

Filter Team and its Protocol pending the execution and return of the search warrant.

 17 Although the Law Firm generally contests the ex parte actions of the government 

below and on appeal, the Firm does not specifically argue that the magistrate judge erred 

by approving the Filter Team and its Protocol in ex parte proceedings before the search 

was conducted. See Br. of Appellant 57; Reply Br. of Appellant 3, 22. We are nevertheless

satisfied that the process by which the authorization was made falls within the Law Firm’s 

broad challenge to the Filter Team and its Protocol. Moreover, we are entitled to assess 

legal issues that have not been squarely raised when it facilitates the correct resolution of 

an appeal. See Meyers v. Lamer, 743 F.3d 908, 912 (4th Cir. 2014) (emphasizing that “it

is the fundamental province of this Court to decide cases correctly, even if that means 

considering arguments . . . not raised by the parties at all”).
30

Second, the magistrate judge should have declined the government’s ex parte

invitation with respect to the Filter Team, and the judge should have conducted adversarial 

proceedings on whether to authorize the Filter Team and the Filter Protocol. See RSZ 

Holdings AVV v. PDVSA Petroleo S.A., 506 F.3d 350, 356 (4th Cir. 2007) (emphasizing 

that ex parte proceedings are “greatly disfavored”); In re Ingram, 915 F. Supp. 2d 761, 

763-64 (E.D. La. 2012) (assessing briefing from parties on propriety of filter team). In

such contested proceedings, the judge could have been fully informed of the relevant

background on the Law Firm and its clients, as well as the nature of the seized materials. 

Additionally, the clients of the Law Firm and their lawyers could have been heard by the 

judge. 

In a recent example involving a proposed filter team, federal agents searched the 

office of Michael Cohen, a New York City lawyer, and seized privileged materials. See

Cohen v. United States, No. 1:18-mj-03161 (S.D.N.Y. Apr. 13, 2018), ECF No. 6 at 4, 25. 

Four days after the search — and before the filter team created by the search warrant had 

reviewed any of the seized materials — the district court conducted adversarial proceedings 

concerning the prosecutor’s proposed use of a filter team. See generally Cohen, ECF No. 

36 (May 1, 2018). Prior to those proceedings, the court was informed of the materials that 

had been seized from Cohen’s office. See Cohen, ECF No. 6 at 18-19. During the 

proceedings, the court heard from Cohen’s lawyer and the lawyer for Cohen’s primary 

client, who each argued against court approval of the filter team request. See Cohen, ECF 

No. 36 at 12-16, 30-31. 
31

The sensible procedures adhered to by the Cohen court demonstrate that, if the 

magistrate judge had conducted adversarial proceedings after the search but before 

approving the Filter Team and its Protocol in this case, the judge would have been fully 

informed of the materials that were seized from the Law Firm. The judge would then have

heard from the Law Firm’s counsel, and possibly also from the clients of the Firm through 

their lawyers, before the Filter Team reviewed any seized materials. The upshot is that —

in failing to conduct adversarial proceedings prior to authorizing the Filter Team and its 

Protocol — the magistrate judge prematurely granted the ex parte request of the United 

States Attorney.18

3.

a.

We are also troubled that, in summarily approving the Filter Team and its Protocol, 

the magistrate judge — like the district court in thereafter assessing the Injunction Requests

— gave no indication that she had weighed any of the important legal principles that protect

attorney-client relationships. Put simply, the Filter Protocol authorized government agents 

and prosecutors to rummage through Lawyer A’s email files. Again, many of the emails

 18 The process adhered to by the Cohen court is pertinent to these proceedings in 

several material respects. For example, the Cohen filter team did not review any of the 

seized materials prior to an adversarial hearing and a ruling on the filter team’s propriety. 

Importantly, the court heard from Cohen’s lawyer and counsel for Cohen’s primary client 

in those proceedings. The court ultimately rejected the government’s filter team proposal 

and appointed a special master. See Cohen, ECF No. 30 (Apr. 27, 2018). Notably, the 

Cohen proceedings were conducted more than a year before the magistrate judge’s 

authorization of this Filter Team.
32

concerned other clients and other matters. The court’s authorization of such an extensive 

review of client communications and lawyer discussions by government agents and 

prosecutors was made in disregard of the attorney-client privilege, the work-product 

doctrine, and the Sixth Amendment. See Klitzman, Klitzman & Gallagher v. Krut, 744 

F.2d at 961 (criticizing seizures of client files from law firm because government made no 

effort to limit seizures of firm’s materials, and thereby “trampl[ed]” on attorney-client

privilege and work-product protections as to all clients); United States v. Stewart, No. 1:02-

cr-00396, 2002 WL 1300059, at *5, *10 (S.D.N.Y. June 11, 2002) (explaining that search 

of lawyer’s office raised Sixth Amendment concerns and appointing special master where 

documents seized from law firm were likely to contain privileged information relating to 

criminal defendants). The magistrate judge erred in failing to explicitly weigh those 

foundational principles that protect attorney-client relationships.

b.

At this juncture, we emphasize another “serious defect” of the Filter Protocol

challenged by the Law Firm as subverting attorney-client relationships. See Reply Br. of 

Appellant 14 n.4. Specifically, the Filter Protocol prospectively authorized the Filter Team 

to contact the Law Firm’s clients ex parte and seek waivers of their attorney-client 

privileges. The Model Rules of Professional Conduct, however, generally bar a lawyer 

from communicating with a represented party about the subject of the representation 

without the represented party’s lawyer being present. See Model Rules of Prof’l Conduct 

r. 4.2 (Am. Bar Ass’n 1983); 2 Hazard, Jr. et al., supra, § 41.02 (explaining that Rule 4.2 

“prevents a lawyer from taking advantage of a lay person”); id. § 41.12 (discussing 
33

application of Rule 4.2 to prosecutors). Although an exception to that rule can — in the 

proper circumstances — be made by a court, any such court order should be predicated on 

an individualized assessment of the attorney-client relationship. See Model Rules of Prof’l 

Conduct r. 4.2; see also United States v. Lopez, 4 F.3d 1455, 1462 (9th Cir. 1993) 

(explaining that court must make “informed decision” regarding whether to authorize 

lawyer’s communication with represented party). That was not even attempted here, in 

that the Filter Protocol was approved ex parte before the search warrant was executed. 

By asking the Law Firm to furnish the Filter Team with a client list — which could

be used by Filter Team members to directly contact clients and seek privilege waivers

under the Filter Protocol — the government demonstrated a lack of respect for the attorneyclient privilege and the Firm’s duty of confidentiality to its clients. In declining to reveal

a client list to the Filter Team, the Law Firm relied on its ethical obligations to protect

confidential and privileged information relating to its clients. See Br. of Appellant 37 

(asserting that the government’s request for a client list ignored the proposition that the 

Law Firm is “ethically prohibited from disclosing . . . the identity of clients when the 

relationship remains confidential”); see also Model Rules of Prof’l Conduct r. 1.6(a) 

(describing duty of confidentiality). Such information will sometimes include the 

existence of the lawyer-client relationship itself. See In re Grand Jury Subpoena, 204 F.3d 

516, 520 (4th Cir. 2000) (recognizing that the attorney-client privilege can “extend to the 

client’s identity”); 1 Hazard, Jr. et al., supra, § 10.12 (collecting cases where client identity 

considered confidential or privileged). The breach of the duty of confidentiality “is 

enforceable by civil remedies as well as through the [attorney] disciplinary process.” See 
34

1 Hazard, Jr. et al., supra, § 10.16, 10-108.1. And a breach of the attorney-client privilege 

by an attorney is likewise sanctionable. See id. Indeed, at least one jurisdiction imposes 

criminal penalties for improperly breaching attorney-client privilege. See Tenn. Code Ann. 

§ 23-3-107. In short, authorizing the government in ex parte proceedings to directly 

contact any and all clients of the Law Firm is another example of how the Filter Protocol 

approved by the magistrate judge undermined attorney-client principles.

4.

At bottom, the magistrate judge erred in assigning judicial functions to the Filter 

Team, approving the Filter Team and its Protocol in ex parte proceedings without first 

ascertaining what had been seized in the Law Firm search, and disregarding the

foundational principles that serve to protect attorney-client relationships. In these 

circumstances, we are satisfied that the magistrate judge (or an appointed special master)

— rather than the Filter Team — must perform the privilege review of the seized materials. 

See Klitzman, Klitzman & Gallagher, 744 F.2d at 962 (recommending appointment of 

special master in similar circumstances); United States v. Gallego, No. 4:18-cr-01537, slip 

op. at 5-6 (D. Ariz. Sept. 6, 2018), ECF No. 65 (appointing a special master “to review the 

items seized from [the] [d]efendant’s law office for privilege and responsiveness to the 

search warrant”); Cohen, ECF No. 30 (Apr. 27, 2018) (appointing special master to review 

documents seized from lawyer); Stewart, 2002 WL 1300059, at *10 (appointing special 

master to perform privilege review of documents seized from office of criminal defense 
35

lawyer).

19 We are therefore satisfied that the Law Firm has demonstrated that it is likely 

to succeed on the merits.

C.

In order to prevail on the next injunction factor, the Law Firm is obliged to show 

that the equities weigh in its favor. See Winter, 555 U.S. at 20. And we are satisfied that 

the Law Firm has done so. Specifically, the harm to the Law Firm and its clients that will 

be caused by continuing the Filter Team’s review outweighs any harm to the government 

that might result from the magistrate judge conducting the privilege review of the seized 

materials. Indeed, we discern no harm to the government in barring the Filter Team from 

rummaging through Law Firm materials that are unrelated to the underlying investigations.

In seeking to convince us otherwise, the government maintains that the magistrate 

judge’s review of the seized materials will unduly delay the government’s investigations. 

And the government claims that it has an interest in efficiently investigating criminal 

wrongdoing. Although efficient criminal investigations are certainly desirable, we are not 

persuaded that the claimed delay in its investigations weighs in the government’s favor. 

Put simply, the government chose to proceed by securing a search warrant for the Law 

Firm and seeking and obtaining the magistrate judge’s approval of the Filter Protocol. The 

 19 The government contends on appeal that the Filter Team’s privilege review of the 

seized materials is no different than such a review by a magistrate judge or a courtappointed special master. Unlike the Filter Team, however, a magistrate judge and a 

special master are judicial officers and neutral arbiters that have no stake in the outcome 

of the privilege decisions. See In re Grand Jury Subpoenas, 454 F.3d at 523 (explaining 

inherent conflict in authorizing filter team to decide privilege claims).
36

government should have been fully aware that use of a filter team in these circumstances

was ripe for substantial legal challenges, and should have anticipated that those challenges

could delay its investigations.

20 And, in any event, delay in the government’s 

investigations here does not outweigh the harm to the Law Firm and its clients caused by 

the Filter Team’s review. See In re Grand Jury Subpoenas, 454 F.3d at 523-24.

The government also argues that the equities weigh against the Law Firm because 

the Firm waited ten days after the search to file its Injunction Requests. We are 

unconvinced, however, that the Law Firm somehow slumbered on its rights. Indeed, the 

Law Firm contested the search and seizures when they were ongoing and — three days 

thereafter — dispatched a detailed letter to the United States Attorney objecting to what 

had occurred and what was apparently going on with the Filter Team. The prosecutors

ignored that letter, prompting the Law Firm to file its Injunction Requests. We do not fault

the Law Firm for seeking a negotiated resolution of these important disputes before 

requesting court intervention. And we will not reward the government for ignoring those 

efforts. See Koster v. Lumbermens Mut. Cas. Co., 330 U.S. 518, 522 (1947) (“[H]e who 

seeks equity must do equity.”). In these circumstances, the Law Firm has convincingly

shown that the equities weigh in its favor.

D.

 20 Notwithstanding the government’s responsibility for some of the delay about 

which it complains, we are nevertheless sensitive to its concerns. Indeed, we have 

expedited this appeal, and we issued our Interim Order within two days of the oral 

argument.
37

Finally, the Law Firm is obliged to establish, in order to secure the relief it seeks,

that “an injunction is in the public interest.” See Winter, 555 U.S. at 20. We are satisfied 

that an award of injunctive relief in these circumstances supports the “strong public 

interest” in the integrity of the judicial system. See United States v. Hasting, 461 U.S. 499, 

527 (1983) (Brennan, J., concurring in part and dissenting in part). By creating

appearances of unfairness to the Law Firm clients who are unrelated to the government’s 

investigation of Client A, the Filter Team and its Protocol contravene the public interest. 

See Gallego, slip op. at 4-6 (recognizing appearances of unfairness inherent in use of filter 

teams and appointing special master to review materials seized from law firm); Stewart, 

2002 WL 1300059, at *8 (explaining that “it is important that the procedure adopted [for 

the review of seized materials] . . . not only be fair but also appear to be fair”); United 

States v. Neill, 952 F. Supp. 834, 841 n.14 (D.D.C. 1997) (emphasizing that use of filter 

team creates “appearance of unfairness”). For those clients — and to the public at large —

it surely appears, as the Sixth Circuit recognized, that “the government’s fox [has been] 

left in charge of the [Law Firm’s] henhouse.” See In re Grand Jury Subpoenas, 454 F.3d 

at 523; see also In re Search Warrant for Law Offices Executed on Mar. 19, 1992, 153 

F.R.D. 55, 59 (S.D.N.Y. 1994) (“It is a great leap of faith to expect that members of the 

general public would believe any . . . wall [between a filter team and a prosecution team]

would be impenetrable; this notwithstanding our own trust in the honor of an AUSA.”). 

Appearances of unfairness are especially apparent in these proceedings, in that the 

Filter Team includes prosecutors employed in the same judicial district where Law Firm

clients “are being investigated by, or are being prosecuted by,” the United States Attorney
38

for Maryland. See S.J.A. 66. It would be difficult for reasonable members of the public to 

believe that Filter Team AUSAs would disregard information in Lawyer A’s emails that 

might be relevant to other criminal inquiries in Maryland. In fact, the government has 

never disclaimed an intention to use the plain-view doctrine in connection with the Filter 

Team’s access to the materials seized from the Law Firm. See United States v. Rumley, 

588 F.3d 202, 205 (4th Cir. 2009) (explaining that, under the plain-view doctrine, a law 

enforcement officer can make a seizure of an object in plain view if, inter alia, “the object’s 

incriminating character is immediately apparent” (internal quotation marks omitted)); cf.

United States v. Comprehensive Drug Testing, Inc., 621 F.3d 1162, 1178 (9th Cir. 2010) 

(Kozinski, C.J., concurring) (suggesting that, “[w]hen the government wishes to obtain a 

warrant to examine a[n] . . . electronic storage medium to search for certain incriminating 

files, . . . magistrate judges should insist that the government forswear reliance on the plainview doctrine” (citation omitted)).21

Due to the appearances of unfairness caused by the Filter Team, and in view of the 

other problems associated with the Filter Team, it is surprising that the government has so 

vigorously supported it. We simply observe that prosecutors have a responsibility to not 

only see that justice is done, but to also ensure that justice appears to be done. See In re 

 21 Even if the Filter Team AUSAs have been instructed to ignore information 

relating to possible criminal activity by other Law Firm clients in the seized materials, our 

plain view concerns would not be assuaged. The review of such information by the Filter 

Team AUSAs cannot be undone. Additionally, the IRS and DEA agents on the Filter Team

have their own superiors. It may well be difficult for those agents to withhold from their 

superiors information about possible crimes potentially identified in the seized materials.
39

Search Warrant for Law Offices, 153 F.R.D. at 59 (“The appearance of [j]ustice must be 

served, as well as the interests of [j]ustice.”). Federal agents and prosecutors rummaging 

through law firm materials that are protected by attorney-client privilege and the workproduct doctrine is at odds with the appearance of justice.

* * *

As reflected herein, we are satisfied that the magistrate judge’s authorization of the 

Filter Team and the Filter Protocol was improper and that injunctive relief is warranted. 

The district court thus abused its discretion by failing to enjoin the Filter Team’s review of 

the seized materials.

22

IV.

Pursuant to the foregoing and our Interim Order, we reverse the district court’s 

Denial Order and remand for such other and further proceedings as may be appropriate.

REVERSED AND REMANDED

 22 Although the Law Firm has raised Fourth Amendment contentions, we leave those 

issues to the district court. See Lovelace v. Lee, 472 F.3d 174, 203 (4th Cir. 2006) 

(emphasizing that this Court is “a court of review, not of first view” (internal quotation 

marks omitted)).
40

RUSHING, Circuit Judge, concurring:

As the majority correctly concludes, the unique facts and circumstances of this case 

preclude this Filter Team operating under this Filter Protocol from reviewing the fruits of 

this search warrant. I write separately to expand upon two points in our analysis of the 

Law Firm’s likelihood of success on the merits. 

First, as the majority notes, after the July 10, 2019 hearing on the Law Firm’s and 

Client A’s pending motions, the district court modified the Privilege Assessment Provision

of the Filter Protocol. Maj. Op. 12. Under the Modified Privilege Assessment Provision, 

no documents—including those the Filter Team considers nonprivileged—can be sent to 

the Prosecution Team without either the consent of the Law Firm or a court order. The 

majority does not suggest that the Modified Privilege Assessment Provision, which 

replaced the original Privilege Assessment Provision, impermissibly usurps a judicial 

function. See Maj. Op. 25–29. 

Second, the Filter Team immediately began reviewing the documents seized from 

the Law Firm, despite the Law Firm’s protests about the attorney-client privilege and workproduct doctrine. In other cases, the government has voluntarily delayed review for a brief 

time until the court could schedule a hearing on the target’s motion for a restraining order 

or injunction. See, e.g., Cohen v. United States, No. 1:18-mj-03161 (S.D.N.Y. Apr. 13, 

2018), ECF Nos. 6, 36. That sensible procedure preserves the status quo until a court can 

rule. The majority suggests a procedure by which a magistrate judge could authorize a 

search but delay ruling on proposed review protocols until the court can sua sponte gather 

the parties for an adversary proceeding. Maj. Op. 29–31. That innovative procedure may 
41

be salutary in some circumstances, but the burden remains on the parties to voice their 

objections, and accommodate the orderly resolution of those objections, in the normal 

course.