22-969-cv

Callahan v. County of Suffolk

1 

In the

United States Court of Appeals

For the Second Circuit

August Term 2023 

No. 22-969 

CHRISTOPHER CALLAHAN, Individually and as Administrator D.B.N. of the 

Estate of Kevin Callahan, 

Plaintiff-Appellant,

PATRICIA CALLAHAN, Individually, 

 Plaintiff, 

v. 

THE COUNTY OF SUFFOLK, POLICE OFFICER THOMAS WILSON, #5675, 

SERGEANT SCOTT GREENE, #960, DETECTIVE RIVERA, DETECTIVE 

O’HARA, JOHN DOE, SUFFOLK COUNTY POLICE OFFICERS # 1-10, 

RICHARD ROE, SUFFOLK COUNTY EMPLOYEES # 1-10, 

Defendants-Appellees, 

POLICE OFFICER ROBERT KIRWAN, #2815, POLICE OFFICER JAMES 

BOWEN, #1294, DETECTIVE SERGEANT THOMAS M. GRONEMAN, 

DETECTIVE LIEUTENANT GERARD PELKOFSKY, 

 Defendants. 

Appeal from the United States District Court

for the Eastern District of New York 

No. 12 Civ. 2973 (GRB), Gary R. Brown, District Judge, Presiding.
22-969-cv

Callahan v. County of Suffolk

2 

(Argued October 11, 2023; Decided March 19, 2024) 

Before: PARKER, LEE, and MERRIAM, Circuit Judges.

Plaintiff-Appellant Christopher Callahan appeals from a judgment of the 

United States District Court for the Eastern District of New York (Brown, J.) 

granting summary judgment to Defendants-Appellees Thomas Wilson and 

Suffolk County on Callahan’s claims under 42 U.S.C. § 1983 for excessive force 

and Monell v. Department of Social Services, 436 U.S. 658 (1978) liability and 

denying Callahan leave to amend to his complaint. 

On appeal, Callahan contends that the district court erred in considering 

and granting summary judgment because, following an earlier appeal in Callahan 

v. Wilson, 863 F.3d 144 (2d Cir. 2017), this Court remanded with instructions to 

hold a new trial. That trial was never held. Callahan also contends that, in any 

event, triable issues of material fact precluded summary judgment. We agree 

with Callahan on both grounds. However, we see no error in the denial by the 

district court on remand of his motion to amend the complaint. Accordingly, we 

VACATE in part, AFFIRM in part, and REMAND for a new trial. 

ALEXANDER KLEIN (Donna Aldea, on the brief), Barket Epstein Kearon 

Aldea & LoTurco, LLP, Garden City, NY, for Plaintiff-Appellant

BRIAN C. MITCHELL, Assistant County Attorney for Christopher J. Clayton, 

Suffolk County Attorney, Hauppauge, NY, for Defendants-Appellees

BARRINGTON D. PARKER, Circuit Judge: 

Plaintiff-Appellant Christopher Callahan appeals from a judgment of the 

United States District Court for the Eastern District of New York (Brown, J.), 
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Callahan v. County of Suffolk

3 

granting summary judgment to Defendants-Appellees Suffolk County Police 

Officer Thomas Wilson and the County of Suffolk on claims under 42 U.S.C. 

§ 1983 related to the death of his brother, Kevin Callahan. This case comes before 

us after more than ten years of litigation in front of four different district court 

judges, a jury trial, and a prior appeal to this Court. Suffice it to say that the 

underlying events are sharply contested. 

In September 2011, Wilson fired four shots, three of which hit and killed 

Kevin Callahan. That is where the parties’ agreement as to what happened 

largely begins and ends. The parties sharply dispute what immediately 

precipitated the shooting and the circumstances surrounding Wilson’s use of 

lethal force and, as a result, his entitlement to qualified immunity. 

However, this appeal turns on a much simpler issue: whether, after a jury 

verdict has been appealed and this Court has vacated the verdict and remanded 

for a new trial, a district court is free to entertain and grant a motion for 

summary judgment. We hold that, under these circumstances, the district court 

violated the mandate rule. Accordingly, we VACATE in part, AFFIRM in part, 

and, again, REMAND for a new trial.1

1 The district court granted summary judgment on not only the 42 U.S.C. § 1983 

claim against Wilson but also the Monell v. Department of Social Services, 436 U.S. 
22-969-cv

Callahan v. County of Suffolk

4 

BACKGROUND 

 On September 20, 2011, Patricia Callahan had a disconcerting call with 

Kevin Callahan, her 26-year-old son. Kevin had substance abuse issues, and 

when he had recently returned to her home in Selden, New York after being 

discharged from the hospital, she chose to leave and stay at a hotel to avoid 

further conflict with him. During the September 20th call, she heard someone 

yelling, and Kevin told her, “Mom, he’s got a gun.” Christopher Callahan was 

with his mother at the time, and, prompted by their concerns arising from the 

call, he contacted the Suffolk County Police Department. 

Three Suffolk County Police officers, including Thomas Wilson, responded 

to a radio dispatch to follow up at Patricia Callahan’s home. Wilson testified that 

he knocked loudly and announced the police presence before entering. Once 

inside, the officers split up, with Wilson and another officer heading downstairs. 

Wilson testified that as he searched the downstairs area, he saw someone 

through the door jamb to a room, and after he had announced himself as an 

658 (1978) claim against the County of Suffolk. Callahan v. Cnty. of Suffolk, 602 

F. Supp. 3d 399, 412-13 (E.D.N.Y. 2022). Because we conclude that granting 

summary judgment violated our mandate to hold a new trial and otherwise was 

not warranted, all claims that were disposed of at summary judgment should 

proceed to trial. 
22-969-cv

Callahan v. County of Suffolk

5 

officer, the person behind the door “start[ed] to square off towards the door.” 

App’x 131-32. Wilson testified that the door then closed on him, pinning him 

between the door and the door frame with part of his left side, including his 

hand carrying his semiautomatic pistol, exposed on the other side of the door. 

Wilson also testified that he heard a “growling sound” and saw “a hand 

thrusting towards [him] with an object.” App’x 170. According to Wilson, he 

feared that the person on the other side of the door had a weapon and that he 

would be killed, so he fired his gun. Wilson testified that after he fired the first 

shot, the door let up and he fell backwards, and as he fell, he continued firing. 

Emergency Services and additional police officers arrived roughly 20 minutes 

later; they found Kevin Callahan unresponsive. App’x 273, 294-95. No weapon 

was found in the room where Kevin Callahan was located. App’x 294-95. An 

autopsy report determined that Kevin Callahan died of three gunshot wounds. 

In June 2012, plaintiffs2 commenced this action in the Eastern District of 

New York against Suffolk County, Wilson, and other Suffolk County Police 

officers and county employees, alleging multiple state and federal law claims, 

2 We refer to plural “plaintiffs” because both Christopher and Patricia Callahan 

were plaintiffs, but Christopher Callahan is the sole plaintiff-appellant.
22-969-cv

Callahan v. County of Suffolk

6 

including claims under 42 U.S.C § 1983. See Complaint, Callahan v. Cnty. of 

Suffolk, No. 12-cv-02973 (“District Court Docket”) (E.D.N.Y. June 14, 2012), ECF 

No. 1. In July 2015, plaintiffs proceeded to trial, including on the claim of 

excessive force against Wilson. The jury returned a verdict in favor of Wilson. 

Plaintiffs appealed to this Court, principally arguing that a new trial was 

required because the jury had not been properly instructed on the excessive force 

claim against Wilson. See Callahan v. Wilson, 863 F.3d 144, 148-52, 154 (2d Cir. 

2017). At trial, the jury had been instructed: “A police officer may use deadly 

force against a person if a police officer has probable cause to believe that the 

person poses a significant threat of death or serious physical injury to the officer 

or others.” Id. at 150 (emphases added). This Court agreed with plaintiffs that 

the jury instruction was inconsistent with our decision in Rasanen v. Doe, 723 F.3d 

325 (2d Cir. 2013), where we held that a “jury ‘must’ be instructed that the use of 

deadly force is ‘unreasonable unless the officer had probable cause to believe that 

the suspect posed a significant threat of death or serious physical injury to the 

officer or to others.’” Id. at 151 (quoting Rasanen, 723 F.3d at 334). As this Court 

noted, the jury instruction in Rasanen “was insufficient because it did not convey 

that an officer’s use of deadly physical force is reasonable, and therefore legally 
22-969-cv

Callahan v. County of Suffolk

7 

permissible, only in a specific circumstance.” Id. We concluded that the jury 

instruction in the Callahan trial posed the same problem. The “fatal defect” was 

that the instruction allowed the jury to find in Wilson’s favor “without 

concluding that Officer Wilson had probable cause to believe that Callahan 

posed a threat of death or serious injury.” Id. at 152 (quoting Rasanen, 723 F.3d at 

336 in the first instance).3 Accordingly, we vacated the judgment and remanded 

for a new trial. Our mandate ordered: “[T]he judgment of the district court is 

VACATED and the case is REMANDED for a new trial.” Judgment Mandate, 

Callahan v. Cnty. of Suffolk, No. 16-336 (2d Cir. Aug. 2, 2017), ECF No. 114. 

However, no new trial was ever held. In May 2018, the parties advised the 

district court that the only remaining unresolved issues were the excessive force 

claim against Wilson and the Monell claim against Suffolk County. See Status 

Report, District Court Docket (May 10, 2018), ECF No. 84. In April 2021, the case 

was reassigned to Judge Brown, and in September 2021, he placed the case on his

trial-ready calendar. 

3 This Court then concluded that this error was not harmless because it “allowed 

the jury to return a defense verdict if it found that Wilson acted according to an 

overly general standard of ‘reasonableness’ that does not comport with the 

holding of Rasanen—that deadly force in this context is reasonable only if the 

requisite probable cause standard is satisfied.” Id. at 152. 
22-969-cv

Callahan v. County of Suffolk

8 

However, the district court was also willing to entertain summary 

judgment motions. In December 2021, the defendants moved for summary 

judgment, arguing that Wilson’s use of deadly force was protected by qualified 

immunity. Shortly thereafter, on January 26, 2022, plaintiffs moved to amend 

their complaint to add a state law claim for battery and to assert that Suffolk 

County was liable under the doctrine of respondeat superior. See Motion to 

Amend Complaint, District Court Docket (Jan. 26, 2022), ECF No. 93. 

On April 29, 2022, the district court granted defendants’ motion for 

summary judgment, finding that plaintiffs had failed to adequately challenge 

defendants’ version of the events that led to Kevin Callahan’s death and 

concluding that “there is no genuine dispute as to any material fact regarding the 

manner in which Wilson shot Callahan.” Callahan v. Cnty. of Suffolk, 602 F. Supp. 

3d 399, 410 (E.D.N.Y. 2022). Accepting Wilson’s version of events, the district 

court held that “his use of lethal force is protected by qualified immunity.” Id. at 

412.4 The district court also denied plaintiffs’ motion to amend the complaint, 

concluding, among other reasons, that, in light of a lengthy delay in seeking to 

4 The district court also granted defendants’ motion for summary judgment with 

respect to the Monell claim against Suffolk County, concluding that plaintiffs had 

waived the claim and, even if they had not, their evidence failed to establish 

Suffolk County’s liability. Id. at 412-13. 
22-969-cv

Callahan v. County of Suffolk

9 

amend, they had not established good cause under Federal Rule of Civil 

Procedure 16(b). Id. at 413-15. This appeal followed.

DISCUSSION 

I. The Mandate Rule’s Preclusion of Summary Judgment 

“We review de novo whether the District Court has complied with our 

mandate.” Puricelli v. Argentina, 797 F.3d 213, 218 (2d Cir. 2015). In our review, 

we “consider both the express terms and broader spirit of the mandate to ensure 

that its terms have been ‘scrupulously and fully carried out.’” Id. (quoting Ginett 

v. Comput. Task Grp., Inc., 11 F.3d 359, 361 (2d Cir. 1993)). 

On appeal, Christopher Callahan contends that the district court’s 

adjudication of the summary judgment motion violated the mandate’s 

instruction to conduct a new trial. He also argues that, in any event, the district 

court erred in granting summary judgment because of the existence of disputed 

issues of material fact. He is correct as to both issues. 

The mandate rule is well-established.5 Under the mandate rule, “[w]here a 

case has been decided by an appellate court and remanded, the court to which it 

5 “The ‘mandate rule’ has existed since the ‘earliest days’ of the judiciary.” In re 

Coudert Bros. LLP (“Coudert Bros.”), 809 F.3d 94, 98 (2d Cir. 2015) (quoting Briggs 

v. Pa. R.R. Co., 334 U.S. 304, 306 (1948)). 
22-969-cv

Callahan v. County of Suffolk

10 

is remanded must proceed in accordance with the mandate . . . as was 

established by the appellate court.” Kerman v. City of New York, 374 F.3d 93, 109 

(2d Cir. 2004) (quotation marks and citations omitted).6 In cases “where a 

mandate directs a district court to conduct specific proceedings and decide 

certain questions, generally the district court must conduct those proceedings 

and decide those questions.” Puricelli, 797 F.3d at 218. In other words, the 

district court “must follow the mandate issued by an appellate court,” and it “has 

no discretion in carrying out the mandate.” Id. (quoting In re Ivan F. Boesky Sec. 

Litig., 957 F.2d 65, 69 (2d Cir. 1992) in the second instance).7

6 The mandate rule is a branch of the law of the case doctrine. United States v. 

Aquart, 92 F.4th 77, 87 (2d. Cir. 2024). The other branch of the law of the case 

doctrine is “implicated when a court reconsiders its own ruling in the absence of 

an intervening ruling of a higher court,” and in such cases, “when a court has 

ruled on an issue, that decision should generally be adhered to by that court in 

subsequent stages in the same case.” Prisco v. A & D Carting Corp., 168 F.3d 593, 

607 (2d Cir. 1999) (quotation marks and citations omitted). This branch is not 

directly relevant to the case before us.

7 Put slightly differently, “the lower court must carry out its duty to give the 

mandate ‘full effect,’” and “cannot vary it, or examine it for any other purpose 

than execution; or give any other or further relief; or review it, even for apparent 

error, upon any matter decided on appeal; or intermeddle with it, further than to 

settle so much as has been remanded.” Coudert Bros., 809 F.3d at 98 (first quoting 

Ginett, 11 F.3d at 360-61; then quoting In re Sanford Fork & Tool Co., 160 U.S. 247, 

255 (1895)). 
22-969-cv

Callahan v. County of Suffolk

11 

We recognize that there are cases where the language and scope of the 

mandate requires the district court to devote some additional analysis to 

determine what it may (and may not) consider on remand. In addition, we have

made clear that “[w]hen the mandate leaves issues open, the lower court may 

dispose of the case on grounds not dealt with by the remanding appellate court.” 

Coudert Bros., 809 F.3d at 98.8 But here, our mandate was quite clear: the district 

court must hold a new trial. 

Further, we also recognize that there may be rare exceptions that justify a 

divergence from a mandate. See, e.g., Wakefield v. N. Telecom, Inc., 813 F.2d 535, 

539-40 (2d Cir. 1987) (noting that, notwithstanding the remand for a new trial, “if 

further discovery proceedings on remand had revealed an undisputed fact 

conclusively precluding the entry of judgment in [the plaintiff’s] favor,” the

district court could have granted summary judgment against him), abrogated on 

other grounds by Pioneer Inv. Servs. Co. v. Brunswick Assocs. Ltd. P’ship, 507 U.S. 380 

8 For example, in Sompo Japan Ins. Co. of Am. v. Norfolk S. Ry. Co. (“Sompo Japan”), 

762 F.3d 165, 172 (2d Cir. 2014), in the original appeal, this Court vacated the 

district court’s grant of summary judgment to the plaintiffs and remanded “for 

further proceedings.” The plaintiffs appealed following the remand, arguing 

that the district court violated the mandate rule by considering newly-raised 

defenses. Id. at 172-73, 175-76. We rejected this argument, concluding that 

nothing in our remand order restricted the district court from considering these

defenses or from addressing issues not decided by this Court. Id. at 175-76. 
22-969-cv

Callahan v. County of Suffolk

12 

(1993). However, circumstances in which a district court may diverge from an 

explicit mandate are very limited, and doing so is reserved for situations when 

developments occurring after a mandate issued would make the mandated 

conduct pointless or clearly irrational. Cf. United States v. Bryson, 229 F.3d 425, 

426 (2d Cir. 2000) (per curiam). 

Here, no exceptional changes to the applicable law or to the facts occurred 

that would warrant a departure from the mandate. Indeed, at argument, 

Callahan’s counsel confirmed that there was no discovery or fact development 

between the issuance of this Court’s mandate and the district court’s grant of 

summary judgment. See Oral Argument Transcript 7:00-7:37. The record upon 

which the district court granted summary judgment was essentially the same as 

the record upon which we had ordered a new trial. Accordingly, there was no 

basis for the district court to disregard our mandate. See Kerman, 374 F.3d at 111-

12. 

We are certainly mindful of the fact that the docket of the court on which 

the district judge sits is unusually heavy and that when he inherited the case, it 

had been pending for a very long time. We are also fully aware of the lower 

court’s understandable interest in resolving this case and moving on to others. 
22-969-cv

Callahan v. County of Suffolk

13 

However, these commendable intentions do not trump a mandate from this 

Court. The rule of law and the stability, predictability, and fairness the mandate 

rule produces would be compromised if mandates were viewed as precatory 

rather than as obligatory. Here, the district court should have held a new trial

because our mandate clearly instructed the district court to do so. 

II. The Disputed Issues Precluding Summary Judgment 

Moreover, even if the district court’s entry of summary judgment did not 

violate the mandate, we would still vacate the order because the record 

contained disputed issues of material fact as to whether Wilson was entitled to 

qualified immunity. “We review orders granting summary judgment de novo

and focus on whether the district court correctly concluded that there was no 

genuine dispute as to any material fact and that the moving party was entitled to 

judgment as a matter of law.” Frost v. N.Y.C. Police Dep’t, 980 F.3d 231, 241 (2d 

Cir. 2020) (quoting Chunn v. Amtrak, 916 F.3d 204, 207 (2d Cir. 2019)). In 

addition, we view the evidence in the light most favorable to the party against 

whom summary judgment was granted. NetJets Aviation, Inc. v. LHC Commc’ns, 

LLC, 537 F.3d 168, 178 (2d Cir. 2008).9 

9 “Further, given the difficult problem posed by a suit for the use of deadly force, 

in which the witness most likely to contradict the police officer’s story—the 
22-969-cv

Callahan v. County of Suffolk

14 

The district court concluded that Wilson was entitled to qualified 

immunity based on its acceptance of Wilson’s account of the shooting. While 

portions of plaintiffs’ opposition arguably relied on speculation, the district court 

overlooked, or omitted from consideration, evidence that called Wilson’s version 

into question. 

For example, Wilson testified at trial—and noted in a police report made 

shortly after the shooting—that when he fired his first shot, the gun was at his 

hip/thigh area. However, the Suffolk County criminal analyst testified that he 

believed the first shot to hit Kevin Callahan was a contact shot that entered his 

right side just below the armpit and traveled across the chest. A jury could view 

that evidence as calling into question whether Wilson, in fact, fired from his hip. 

As a result, a jury could call into question Wilson’s account of being trapped by 

someone pushing against the door. In addition, Wilson said he fired one shot 

into the room while he was pinned in the door and that, because the door let up 

person shot dead—is unable to testify, the court may not simply accept what 

may be a self-serving account by the police officer. Rather, the court must also 

consider circumstantial evidence that, if believed, would tend to discredit the 

police officer’s story, and consider whether this evidence could convince a 

rational factfinder that the officer acted unreasonably.” O’Bert ex rel. Est. of 

O’Bert v. Vargo, 331 F.3d 29, 37 (2d Cir. 2003) (citations, brackets, punctuation, 

and quotation marks omitted). 
22-969-cv

Callahan v. County of Suffolk

15 

after the first shot, he continued shooting as he fell back. As such, a jury could 

believe that if the rest of the shots were fired as Wilson fell backwards, the bullets 

would be traveling in an upwards trajectory. But because there is evidence 

indicating that none of the bullets that hit Kevin Callahan was traveling in an 

upwards trajectory, a jury could rely on that evidence to doubt Wilson’s account. 

Moreover, at summary judgment, Callahan submitted an expert report opining 

that two of the three shots that hit Kevin Callahan were fired from inside the 

room, rather than through the door. A jury could find that evidence inconsistent 

with Wilson’s claim that he fell backwards after the first shot, reasoning that if 

Wilson’s account were true, then only one shot should have been fired from 

inside the bedroom. 

Further, the expert evidence revealed that there were significant open 

questions of fact. For example, while the defense’s ballistic expert opined that 

the first shot Wilson fired was against “an individual leaning up against the 

door,” he also testified that, “[w]e can’t say exactly what he [Kevin Callahan] 

might have been doing before [he was shot]. . . . Exactly what would occur 

before that shot got fired cannot be said. There is no forensic crystal ball to 

guarantee how that happened.” App’x 384-85. At summary judgment, plaintiffs 
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Callahan v. County of Suffolk

16 

submitted a report from their expert opining that several factual questions could 

not be conclusively resolved based on the available evidence, including: “[t]he 

exact position of Officer Wilson’s body throughout the incident,” “[t]he exact 

position of Mr. Callahan’s body throughout the incident,” “Mr. Callahan’s 

actions prior to and during the shooting incident,” and “[t]he position of the 

bedroom door throughout the incident.” App’x 609. In view of the conflicting 

testimony and unresolved questions of fact in the record, summary judgment 

was not warranted. 

III. The Denial of the Motion for Leave to Amend the Complaint 

Plaintiff-Appellant also appeals the district court’s denial of his motion to 

amend his complaint. On January 26, 2022, nearly ten years after the start of this 

litigation, plaintiffs moved to amend their complaint to add a state law battery 

claim, asserting that Suffolk County was vicariously liable for Wilson’s actions. 

They sought to do so in light of this Court’s January 21, 2022 decision, Triolo v. 

Nassau County, 24 F.4th 98, 110-13 (2d Cir. 2022), which held that municipalities 

could be vicariously liable under New York state law for an employee’s 

wrongful conduct, even when the employee was entitled to individual qualified 

immunity. Plaintiffs’ justification for the delay was that a claim against Suffolk 
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Callahan v. County of Suffolk

17 

County under a respondeat superior theory would have been superfluous prior to 

Triolo because “Suffolk County was already required to indemnify Officer 

Wilson, leaving no financial benefit to a direct municipal claim.” Appellant’s 

Brief 37. However, the district court denied the motion, concluding that 

plaintiffs did not act with sufficient diligence to satisfy Rule 16(b)(4) because they 

“could have included a respondeat superior claim against the County along with 

their state law tort claims at the time the complaint was filed.” Callahan, 602 F. 

Supp. 3d at 414.10

Although a plaintiff may amend a complaint after a scheduling order 

deadline, under Rule 16(b)(4), the plaintiff may do so only upon a showing of 

good cause. Sacerdote v. New York Univ., 9 F.4th 95, 115 (2d Cir. 2021), cert. denied, 

142 S. Ct. 1112 (2022). “Whether good cause exists turns on the ‘diligence of the 

moving party.’” Holmes v. Grubman, 568 F.3d 329, 335 (2d Cir. 2009) (quoting 

Grochowski v. Phoenix Constr., 318 F.3d 80, 86 (2d Cir. 2003)). Denials of leave to 

amend are typically reviewed for abuse of discretion. Id. at 334. However, 

10 The district court also noted that even if plaintiffs had established good cause, 

it “would still deny the motion to amend the complaint because of the undue 

prejudice of prolonging this litigation for defendants[.]” Callahan, 602 F. Supp. 

3d at 414. Because we affirm the district court’s primary basis for denying leave 

to amend, we decline to address its alternative justification. 
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Callahan v. County of Suffolk

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plaintiffs argue that the denial here should be reviewed de novo because it was 

based on a legal interpretation, namely the interpretation of Triolo. See

Appellant’s Brief 33 (citing Gorman v. Consol. Edison Corp., 488 F.3d 586, 592 (2d 

Cir. 2007)). We do not need to resolve which is the appropriate standard of 

review, because under either, we would affirm the district court’s denial of leave 

to amend. 

Plaintiffs argue that they acted diligently and, thus, satisfied Rule 16(b)’s 

good cause standard. They contend that the proposed amendments were a result 

of a change of law effected by Triolo, 24 F.4th at 110-13, and that they 

expeditiously moved to amend their complaint after Triolo was published. As 

the district court noted, a change in controlling law may provide good cause to 

amend. Callahan, 602 F. Supp. 3d at 413. 

However, here, there was no change in controlling law that impacted 

plaintiffs’ ability to raise their proposed claim at the start of this litigation. 

Although Triolo settled a previously open question regarding municipal liability, 

plaintiffs could have asserted their proposed respondeat superior claim against 

Suffolk County at the time of filing, regardless of Triolo. Apparently, plaintiffs 

chose not to include the proposed respondeat superior claim earlier because they 
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Callahan v. County of Suffolk

19 

believed that the claim offered no potential financial benefit to them, given that 

Suffolk County would indemnify the officers, and the claim would have been 

dismissed if the officers were entitled to qualified immunity. However, nothing 

as a matter of law barred plaintiffs from including the claim. Because plaintiffs 

sought long after this litigation commenced to amend their complaint to add a 

claim that was available at the beginning of it, we agree with the district court 

that they did not move with the diligence needed to satisfy the good cause 

standard of Rule 16(b). Accordingly, we affirm the district court’s denial of leave 

to amend. 

CONCLUSION 

For the reasons set forth above, the judgment of the district court is 

VACATED in part, AFFIRMED in part, and REMANDED once again for a new 

trial.