PRECEDENTIAL

UNITED STATES COURT OF APPEALS

FOR THE THIRD CIRCUIT

No. 23-1939

UNITED STATES OF AMERICA,

v.

SUNNY SOK,

 Appellant

Appeal from the United States District Court

for the Eastern District of Pennsylvania

(District Court No. 2-19-cr-00348-001)

District Judge: Honorable Mitchell S. Goldberg

Argued on June 4, 2024

Before: HARDIMAN, PORTER, and AMBRO, Circuit 

Judges

(Opinion filed August 22, 2024)
2

Abigail E. Horn (Argued)

Federal Community Defender Office for the Eastern District 

of Pennsylvania

601 Walnut Street

The Curtis Center, Suite 540 West

Philadelphia, PA 19106

Counsel for Appellant

Anita D. Eve

Robert A. Zauzmer (Argued)

Office of United States Attorney

615 Chestnut Street

Suite 1250

Philadelphia, PA 19106

Counsel for Appellee

OPINION OF THE COURT

AMBRO, Circuit Judge

A Philadelphia police officer pulled over Sunny Sok 

after he made an illegal right turn. The officer ran a search and 

discovered that the vehicle had an expired registration and also 

that Sok had an arrest warrant for a probation violation. The 

latter turned out not to be true—the warrant was no longer 

active—but before that came to light, the officer arrested Sok. 

While the officer was doing so, he claimed to smell marijuana 
3

emanating from the vehicle, which led him to search it. The 

officer discovered multiple narcotics and a firearm, and Sok 

was subsequently charged with possession with intent to 

distribute a controlled substance, possession of a firearm in 

furtherance of drug trafficking, and possession of a firearm by 

a felon.

Sok moved to suppress the physical evidence seized 

during the search. The District Court determined that the 

officer’s testimony regarding the marijuana odor was not 

credible and, consequently, that there was no probable cause 

for the search. The Court went on, however, to conclude 

suppression was not warranted because the narcotics and 

firearm would inevitably have been discovered under 

Philadelphia’s Live Stop Policy, which requires that 

unregistered vehicles—like Sok’s—be impounded and their 

contents inventoried.

On appeal, Sok argues that the inevitable-discovery 

doctrine does not apply and the evidence should have been 

suppressed, as the Government has not demonstrated that any 

impoundment of his unregistered vehicle would have been 

lawful or inevitable under the Live Stop Policy. But Sok failed 

to raise these suppression-related arguments before the District 

Court. Thus, we cannot consider them unless he shows good 

cause for us to do so. Fed. R. Crim. P. 12(b)(3)(C), (c)(3); see 

United States v. Rose, 538 F.3d 175 (3d Cir. 2008). Because 

he does not make that demonstration, we do not consider his 

untimely arguments and affirm the judgment of his conviction

and sentence.
4

I. Background

Philadelphia Police Officer Joseph Mason pulled Sok 

over for making an illegal right turn in April 2019. Officer 

Mason ran the car’s license plate in police databases. The 

search showed that the vehicle had an expired registration. It

also showed that the owner of the vehicle, Sok, had an arrest 

warrant against him for a probation violation. In fact, there 

was no outstanding warrant, as Mason learned later in the 

encounter. Before that, however, Mason confirmed Sok was 

the owner, asked him to step outside of the vehicle, informed 

him of the outstanding warrant, and placed him in handcuffs. 

As Sok stepped out, he told Mason that the warrant was no 

longer active and told him to call his parole officer to confirm. 

As this occurred, Mason saw two small bottles in the driverside door pocket that “contain[ed] a purple liquid.” App. 99. 

He believed the substance in the bottles was Promethazine 

syrup, a type of cough syrup that is a controlled substance. 

This too turned out to be a mistake. The purple liquid in the 

containers was later tested and was not a controlled substance. 

Sok continued to ask Mason to call his parole officer to 

confirm the warrant was no longer outstanding, but Mason 

proceeded to detain him. He frisked Sok and discovered two 

other small containers on his person, including a pill container.

Mason then placed Sok in the back of his police car. He went 

back to Sok’s vehicle to obtain the two small bottles from the 

driver-side door. As he was doing so, Mason claims to have 

smelled an odor of marijuana coming from the vehicle. This 

was notable because he had not smelled marijuana on his first 

approach. Based on the alleged marijuana smell, Mason 

searched the car. 
5

The search revealed, inter alia, a large bottle with a 

label reading “Promethazine”; two more small bottles 

containing purple liquid, similar to those in the driver-side 

door; a bag of white crystals and powder; a plastic soup 

container containing a green leafy substance; a second soup 

container holding a bag of pills and white powder; and a 

revolver. The various recovered substances were later tested. 

The green, leafy substance was marijuana, and some of the 

containers held marijuana resin. The remaining items included 

a number of controlled substances, including heroin, fentanyl, 

and methamphetamine. But none of the small bottles 

containing the purple liquid or larger bottle labeled as 

“Promethazine” held a controlled substance. After Mason 

discovered the narcotics and firearm in the vehicle, he received 

confirmation that Sok’s probation warrant had been lifted and 

was no longer active. 

In light of the narcotics and firearm, Sok was indicted 

on charges for possession with intent to distribute a controlled 

substance, 21 U.S.C. § 841(a)(1), (b)(1)(A), possession of a 

firearm in furtherance of a drug trafficking crime, 18 U.S.C. 

§ 924(c)(1)(A), and being a felon in possession of a firearm, 18 

U.S.C. § 922(g)(1). He filed a motion to suppress the physical 

evidence seized during the stop, arguing that the officer 

impermissibly extended the stop and there was no probable 

cause supporting his arrest, meaning the seized evidence 

should be excluded under the fruit-of-the-poisonous-tree 

doctrine. See Wong Sun v. United States, 371 U.S. 471, 488

(1963). The Government opposed, arguing that the traffic stop 

was valid, reasonable suspicion existed to extend it, and there 

was probable cause to search the car, based in part on Mason’s 

detecting an odor of marijuana coming from it. The District 

Court then held a suppression hearing. 
6

During the hearing, Mason, in addition to discussing the 

details of the traffic stop outlined above, also testified about 

Philadelphia’s Live Stop Policy concerning the impoundment 

of vehicles. He described how, had he not searched the car 

during the traffic stop, he would have impounded it due to its 

lack of valid registration and thereafter would have conducted 

an inventory search per the Policy.

The Live Stop Policy in effect at the time stated that 

“any vehicle may be impounded when it is determined, during 

a lawful vehicle investigation[,] that the operator is in violation

of any or all” of four Pennsylvania state statutory provisions, 

one of which prohibits driving an unregistered vehicle. App. 

241; see 75 Pa. C.S. §§ 1301(a) (“No person shall drive or 

move . . . any vehicle which is not registered in this 

Commonwealth unless the vehicle is exempt from 

registration.”), 6309.2(a)(2) (“If a motor vehicle . . . for which 

there is no valid registration . . . is operated on a highway or 

trafficway of this Commonwealth, the law enforcement officer 

shall immobilize the motor vehicle . . . or, in the interest of 

public safety, direct that the vehicle be towed[.]”). Despite the 

permissive “may” language quoted above, the Policy later

states that any vehicle in violation of the registration 

requirement, 75 Pa. C.S. § 6309.2, “shall be impounded” 

according to the procedures set out in the Policy (with limited 

exceptions not applicable here). App. 242.1 

1 A newer version of the Policy, effective as of February 18, 

2022, provides that, “[i]n accordance with Pennsylvania case 

law, only vehicles that bear a public safety risk may be subject 

to immediate towing (impoundment).” Philadelphia Police 

Department Directive 12.8, “Live Stop” Program,
7

Under the Policy, once it is determined that a vehicle is 

unregistered during the course of a traffic stop, the officer 

must: (1) confirm the registration status over police radio; (2) 

inform the operator the vehicle is being impounded; (3) prepare 

the relevant report; (4) respond to other priority calls; and (5) 

after the tow truck arrives, complete an inventory search.2 If 

the registration status of the vehicle cannot be confirmed, the 

vehicle will not be impounded. If the officer needs to leave the 

scene prior to arrival of a tow truck, such as by responding to 

a priority call, then the tow truck will be canceled. If the tow 

truck does not arrive within 30 minutes, the officer will simply 

issue a citation rather than tow the vehicle.

After the suppression hearing, the District Court 

ordered supplemental briefing on multiple issues, including

whether Mason’s search of the car would have been legal if the 

Court were to disregard his testimony regarding the marijuana 

odor as well as how the Live Stop Policy “impact[ed] the 

legality of Officer Mason’s search[.]” App. 186. In his 

supplemental brief, Sok argued that there was no probable 

cause for the search because Mason’s testimony regarding the 

marijuana odor was not credible. He also asserted that the Live 

Stop Policy had no effect on the legality of the search because 

https://www.phillypolice.com/assets/directives/D12.8-

VehicleOrPedestrianInvestigations.pdf, App. A at 2 (last 

accessed August 20, 2024) [https://perma.cc/88EJ-ATWC]. 

This caveat was not present in the Policy at the time of Sok’s 

arrest, however.

2 Here, there is no dispute that an inventory search of Sok’s 

vehicle would have occurred after an impoundment under the 

Policy. There is also no dispute about the legality of the scope 

of the potential inventory search.
8

Mason did not actually “conduct a proper ‘live stop,’” so 

“neither the inventory search exception nor the inevitable 

discovery exception to the Fourth Amendment’s Exclusionary 

Rule apply.” App. 197 (citations omitted). The Government 

responded that Mason’s testimony regarding the marijuana 

odor was credible and supported probable cause. It also 

claimed that the Live Stop Policy would inevitably have led to 

the discovery of the incriminating evidence because “the 

controlled substances and firearm would have been discovered 

when officers conducted an inventory search of the vehicle 

pursuant to” the Live Stop Policy. App. 211.

After reviewing the supplemental briefing, the District 

Court denied Sok’s motion to suppress. It first concluded, in 

Sok’s favor, that the warrantless search of his vehicle was not 

supported by probable cause because Mason’s testimony that 

he smelled marijuana emanating from the car was not credible. 

But the Court nonetheless ruled that suppression of the 

physical evidence was not warranted because the inevitablediscovery doctrine applied. Specifically, it determined that

even if Mason had not searched Sok’s car during the traffic 

stop—unlawfully, as it turned out, given the lack of probable 

cause—law enforcement would have discovered the narcotics 

and firearm under the Live Stop Policy because the car would 

have been impounded and then searched for inventory 

purposes. 

Having lost the suppression argument, Sok proceeded 

to a jury trial and was convicted of all three counts noted above. 

He was sentenced to 240 months’ imprisonment and four years 

of supervised release. He appeals from the judgment of his 
9

conviction and sentence.

3

II. Discussion

On appeal, Sok argues that the Government has not 

demonstrated that any impoundment of his vehicle would have 

been lawful or inevitable, meaning the inevitable-discovery 

doctrine does not apply and the physical evidence used against 

him should have been suppressed as being unlawfully seized. 

For his first argument, concerning the lawfulness of the 

potential impoundment under the Live Stop Policy, he 

contends the Government has not demonstrated that an 

impoundment based solely on his vehicle’s expired registration 

would have been reasonable as an exercise of a communitycaretaking function—an exception to the Fourth Amendment’s 

warrant requirement. See United States v. Smith, 522 F.3d 305, 

313–14 (3d Cir. 2008); see also South Dakota v. Opperman, 

428 U.S. 364, 369 (1976) (“The authority of police to seize and 

remove from the streets vehicles impeding traffic or 

threatening public safety and convenience is beyond 

challenge.”). For his second argument, concerning the

inevitability of the potential impoundment under the Live Stop 

Policy, Sok claims that the Government has failed to 

demonstrate that all of the contingencies to impoundment, such 

as a tow truck arriving within the prescribed window of 30 

minutes, would inevitably have occurred to result in the car

being towed and inventoried but for Mason’s illegal search.

The problem is that Sok did not raise these two

3 The District Court had jurisdiction under 18 U.S.C. § 3231. 

We have jurisdiction under 28 U.S.C. § 1291 and 18 U.S.C. 

§ 3742(a).
10

arguments before the District Court. Instead, the only 

argument he made was that the inevitable-discovery doctrine 

did not apply because no impoundment under the Live Stop 

Policy actually occurred. But, as Sok concedes, that sole 

“argument . . . was wrong” because it “speaks to the related but 

distinct independent source doctrine, not inevitable discovery.” 

Reply Br. at 2. The two doctrines differ as follows:

[U]nder the independent source doctrine, 

evidence that was in fact discovered lawfully, 

and not as a direct or indirect result of illegal 

activity, is admissible. In contrast, the inevitable 

discovery doctrine, applied in Nix [v. Williams, 

467 U.S. 431 (1984)], permits the introduction of 

evidence that inevitably would have been 

discovered through lawful means, although the 

search that actually led to the discovery of the 

evidence was unlawful. The independent source 

and inevitable discovery doctrines thus differ in 

that the former focuses on what actually 

happened and the latter considers what would 

have happened in the absence of the initial 

search.

United States v. Herrold, 962 F.2d 1131, 1140 (3d Cir. 1992) 

(emphases in original). While the fact that no impoundment 

actually occurred would be relevant to an independent-source 

defense raised by the Government, it is not relevant to the 

Government’s inevitable-discovery defense raised here.

Yet Sok contends that he functionally made the same or 

similar arguments before the District Court and can reframe 

them on appeal. In this regard, we require litigants to preserve 
11

specific arguments for appeal, not merely issues. United States 

v. Joseph, 730 F.3d 336, 341 (3d Cir. 2013) (“[R]aising an 

issue in the District Court is insufficient to preserve for appeal 

all arguments bearing on that issue. Instead, to preserve a 

suppression argument, a party must make the same argument 

in the District Court that he makes on appeal.”). In other 

words, “raising an issue is not sufficient to preserve all 

arguments within the issue.” Id. Determining whether an 

argument raised on appeal is the same as one raised in the trial 

court requires at least that “they depend on the same legal rule 

or standard” and “on the same facts.” Id. at 342. And while 

“[p]arties are free . . . to place greater emphasis and more fully 

explain an argument on appeal than they did in the District 

Court [and] may even, within the bounds of reason, reframe 

their argument,” “they may not change [its] substance.” Id. at 

341.

Sok simply did not raise, in any form, his two arguments 

against inevitable discovery before the District Court. While

he cited the legal rule for inevitable discovery and noted some 

of the steps in the Live Stop Policy’s procedure for 

impoundment in his supplemental briefing, he did not argue 

that the Government failed to demonstrate an impoundment 

would have been lawful or inevitable. Instead, as discussed,

his trial attorney appears simply to have confused the 

inevitable-discovery and independent-source doctrines. By 

arguing that no impoundment under the Live Stop Policy 

actually occurred, Sok’s trial counsel did not address the 

Government’s inevitable-discovery defense, which relies on 

the premise that an impoundment, although it did not occur, 

would inevitably have occurred under the Policy. Nor did 

Sok’s counsel otherwise attempt to raise the arguments he 

presses here, such as through a motion for reconsideration of 
12

the suppression ruling.

Because Sok failed to raise before the District Court the 

two suppression-related arguments he presses on appeal, we 

cannot consider them under Federal Rule of Criminal 

Procedure 12 unless he shows good cause for us to do so.

A. Rule 12’s “Good Cause” Standard for Untimely 

Arguments

Rule 12 requires that certain “defenses, objections, and 

requests must be raised by pretrial motion if the basis for the 

motion is then reasonably available and the motion can be 

determined without a trial on the merits[.]” Fed. R. Crim. P. 

12(b)(3). Arguments related to the “suppression of evidence” 

are included among the issues that must be raised before trial. 

Id. 12(b)(3)(C). Rule 12 also specifies the consequences for 

failing to raise an argument in a timely motion:

If a party does not meet the deadline for making 

a Rule 12(b)(3) motion, the motion is untimely. 

But a court may consider the defense, objection, 

or request if the party shows good cause.

Fed. R. Crim. P. 12(c)(3). Under that text, Sok’s suppressionrelated arguments are untimely, and we can consider them only

if he shows good cause for us to do so.

Sok counters that we should consider his untimely 

arguments under Federal Rule of Criminal Procedure Rule 

52(b)’s plain-error standard rather than the good-cause 

standard in Rule 12. Rule 52(b) provides that “[a] plain error 

that affects substantial rights may be considered even though it 
13

was not brought to the court’s attention.” Fed. R. Crim. P. 

52(b). In other words, to determine if there is plain error, we 

ask whether there was an “error” that was “plain” and “affects

[the defendant’s] substantial rights.” Id.; see United States v. 

Olano, 507 U.S. 725, 732–35 (1993). Further, we do not 

exercise our discretion to address such an error unless it 

“seriously affect[s] the fairness, integrity or public reputation 

of judicial proceedings.” Olano, 507 U.S. at 732 (internal 

quotation and citation omitted).

Contrary to Sok’s position, however, we have held that 

Rule 12’s good-cause standard of review trumps Rule 52(b)’s 

plain-error standard for issues that must be raised before trial 

under Rule 12. Rose, 538 F.3d at 182–84. Specifically, we 

reasoned that Rule 12 is a narrower provision that “singles out” 

the issues in Rule 12(b)(3), including suppression, and that its 

standard of review thus prevails over that of the more generally 

applicable Rule 52(b). Id. at 182–83; see also In re 

Combustion Eng’g, Inc., 391 F.3d 190, 237 n.49 (3d Cir. 

2004), as amended (Feb. 23, 2005) (noting the “well-settled 

maxim that specific statutory provisions prevail over more 

general provisions”).4

4 At least before the 2014 amendment to Rule 12, discussed 

further below, most courts of appeals followed the approach 

we took in Rose, concluding that Rule 12’s good-cause 

standard applies to untimely Rule 12 arguments raised for the 

first time on appeal rather than Rule 52(b)’s plain-error rule. 

See Rose, 538 F.3d at 180 (describing this as the “prevailing” 

rule (citation omitted)); United States v. Chavez-Valencia, 116 

F.3d 127, 132–33 (5th Cir. 1997) (listing cases); United States 
14

Sok argues that this holding in Rose—i.e., that we 

review untimely Rule 12 arguments only if there is good cause 

to do so and do not review for plain error—does not survive a 

2014 amendment to the text of Rule 12. We disagree. Since 

v. Walker, 665 F.3d at 228 (1st Cir.) (calling it the “majority 

view”).

That said, there were differing approaches to resolving 

the tension between Rule 12 and Rule 52(b) for Rule 12 pretrial 

issues raised for the first time on appeal. Some cases applied 

Rule 52(b)’s plain-error rule, at times without even mentioning 

Rule 12. See, e.g., United States v. Stevens, 487 F.3d 232, 242 

(5th Cir. 2007); United States v. Buchanon, 72 F.3d 1217, 1227 

(6th Cir. 1995); United States v. Moore, 104 F.3d 377, 382 

(D.C. Cir. 1997). Other circuits were at times internally 

inconsistent, sometimes applying Rule 12’s good-cause 

standard and sometimes applying plain-error review. See, e.g.,

Chavez-Valencia, 116 F.3d at 132–33 (identifying “intracircuit conflicts”); United States v. Soto, 794 F.3d 635, 649 

(6th Cir. 2015) (noting intra-circuit inconsistency); United 

States v. Anderson, 783 F.3d 727, 740 (8th Cir. 2015) (same).

The Seventh Circuit sometimes used a mixed solution, 

which first applied Rule 12’s good-cause standard and, if the 

party showed good cause, then determined whether there was 

plain error under Rule 52(b). See, e.g., United States v. King, 

627 F.3d 641, 647 (7th Cir. 2010); United States v. Hargrove, 

508 F.3d 445, 450 (7th Cir. 2007). The Seventh Circuit has 

also applied a different solution altogether, requiring appellate 

courts to ask whether it would have been within the trial court’s 

discretion to reject a Rule 12 argument as untimely if it had 

been raised in the trial court initially. See, e.g., United States 

v. Acox, 595 F.3d 729, 732 (7th Cir. 2010); United States v. 

Kirkland, 567 F.3d 316, 322 (7th Cir. 2009).
15

the 2014 amendment, we have continued to apply the rule that 

suppression arguments raised for the first time on appeal are 

not considered except for good cause. See, e.g., United States 

v. Scarfo, 41 F.4th 136, 169 (3d Cir. 2022), cert. denied sub 

nom. Pelullo v. United States, 143 S. Ct. 1044 (2023). Yet 

because we have not examined the issue at length, we do so 

today.

At the time we decided Rose, Rule 12 provided the 

following consequence for failing to raise a suppression issue 

(or any other Rule 12(b)(3) issue) in a timely fashion:

A party waives any Rule 12(b)(3) defense, 

objection, or request not raised by the deadline 

the court sets under Rule 12(c) or by any 

extension the court provides. For good cause, 

the court may grant relief from the waiver.

Fed. R. Crim. P. 12(e) (prior to 2014 amendment) (emphases 

added). The 2014 amendment to Rule 12 removed the 

“waiver” language from Rule 12(e). See Fed. R. Crim. P. 

12(e). Instead, the consequences for failing to raise timely one 

of the issues listed in Rule 12(b)(3), for which a pretrial motion 

is required, are now described in Rule 12(c)(3), as set out

above.

Sok’s argument relies on the fact that our holding in 

Rose was based in part on the now-removed “waiver” language 

of the former Rule 12(e). See Rose, 538 F.3d at 179–84. 

Specifically, we concluded that Rule 12(e) “mean[t] what it 

sa[id]” and, consequently, suppression arguments raised for the 

first time on appeal are not considered merely forfeited but 

“waived,” meaning they cannot be considered (absent good 
16

cause). Id. at 183. We reached this conclusion while noting 

that the former Rule 12(e)’s use of the term “waiver” sat 

uncomfortably with the distinction between forfeiture and 

waiver drawn by the U.S. Supreme Court in Olano, where the 

Court clarified that “waiver” refers to the “intentional 

relinquishment or abandonment of a known right,” whereas 

“forfeiture” is the “failure to make the timely assertion of a 

right . . . .” 507 U.S. at 733 (internal quotation omitted); see 

Rose, 538 F.3d at 183; see also United States v. Dowdell, 70 

F.4th 134, 140 (3d Cir. 2023) (observing the same distinction

as Olano).5

While the 2014 amendment to Rule 12 removed the 

“waiver” language—and thus rescinds the portion of our 

reasoning in Rose dependent on that language—it did not 

change the standard of review for Rule 12(b)(3) arguments 

raised for the first time on appeal. Those arguments still must 

be raised by the pretrial deadline; if not, they are “untimely.” 

Fed. R. Crim. P. 12(c)(3). And we still can review “untimely” 

5 Under Olano’s distinction between the two terms, the 

inadvertent failure to raise a timely Rule 12(b)(3) argument 

would be treated as a forfeiture rather than a waiver. See Rose, 

538 F.3d at 183 (“Per [Olano], failure to comply with Rule 12 

could be seen as more akin to a forfeiture . . . .”). As such, it 

would be subject to plain-error review. See id.; Fed. R. Crim. 

P. 52(b); see also Olano, 507 U.S. at 733 (“Mere forfeiture, as 

opposed to waiver, does not extinguish an ‘error’ under Rule 

52(b).”). Yet, despite Rule 12(e)’s apparent misuse of the term

“waiver,” we concluded that it nonetheless meant what it said 

and, as a result, we would not review untimely Rule 12 

arguments (not even for plain error) unless there was good 

cause to do so. Rose, 538 F.3d at 183–84.
17

Rule 12(b)(3) arguments only if a party shows “good cause” 

for us to do so. Id. Nothing in the text of Rule 12 after the 

2014 amendment supplants its good-cause standard of review 

in favor of Rule 52(b)’s plain-error standard. This is further 

supported by the Advisory Committee note accompanying the 

2014 amendment, which explains the reason for the removal of 

the “waiver” terminology:

New paragraph (c)(3) governs the review of 

untimely claims, previously addressed in Rule 

12(e). Rule 12(e) provided that a party “waives” 

a defense not raised within the time set under 

Rule 12(c). Although the term waiver in the 

context of a criminal case ordinarily refers to the 

intentional relinquishment of a known right, 

Rule 12(e) has never required any determination 

that a party who failed to make a timely motion 

intended to relinquish a defense, objection, or 

request that was not raised in a timely fashion. 

Accordingly, to avoid possible confusion the 

Committee decided not to employ the term 

“waiver” in new paragraph (c)(3).

Fed. R. Crim. P. 12, Advisory Committee Note to 2014 

Amendment.6 This amendment, the Advisory Committee 

emphasizes, did not change the standard of review for untimely 

6 While not binding on us, the Advisory Committee’s notes are 

“of weight” in our interpretation of the Federal Rules. Moore 

v. Walton, 96 F.4th 616, 624 (3d Cir. 2024) (quoting In re Nat. 

Football League Players Concussion Inj. Litig., 775 F.3d 570, 

577 n.6 (3d Cir. 2014)).
18

arguments:

New paragraph 12(c)(3) retains the existing 

standard for untimely claims. The party seeking 

relief must show “good cause” for failure to 

raise a claim by the deadline, a flexible standard 

that requires consideration of all interests in the 

particular case.

Id. In other words, Rule 12 continues to mean what it says and 

“provides only one circumstance in which an untimely motion 

can be considered—when the movant ‘shows good cause.’” 

United States v. Bowline, 917 F.3d 1227, 1230 (10th Cir. 2019)

(quoting Fed. R. Crim. P. 12(c)(3)).7 Accordingly, Sok must 

meet that measure for us to consider his untimely suppression 

7 We note that some courts of appeals have changed their 

position in light of the 2014 amendment and now use plainerror review for Rule 12 arguments raised for the first time on 

appeal. See, e.g., United States v. Vasquez, 899 F.3d 363, 372–

73 (5th Cir. 2018), as revised (Aug. 24, 2018); Soto, 794 F.3d 

at 648–55 (6th Cir); United States v. Sperrazza, 804 F.3d 1113, 

1118–19 (11th Cir. 2015); see also 1A Charles Alan Wright & 

Arthur R. Miller, Federal Practice and Procedure § 194 & 

nn.22–23 (5th ed. West) (“Some appellate courts now conclude 

that untimely motions should be subject to plain error review 

in the absence of evidence that the defendant intentionally 

relinquished the claim, either because they found the change in 

language in the 2014 amendments significant, or because the 

approach was dictated by circuit precedent.”). Nonetheless, we 

stick with the text of Rule 12, which states that “good cause” 

is the standard of review for untimely Rule 12(b)(3) arguments.
19

arguments.

B. Good Cause

We have not rigidly demarcated what may qualify as

“good cause” to excuse the untimeliness of a Rule 12 argument

raised for the first time on appeal.

8

 The Supreme Court has 

indicated that, as a general matter, a showing of both cause and 

prejudice is necessary on direct appeal and collateral review. 

8

If a district court makes a “good cause” determination for an 

untimely Rule 12 argument in the first instance, we review for 

abuse of discretion. United States v. Desu, 23 F.4th 224, 232 

(3d Cir. 2022); see also Davis v. United States, 411 U.S. 233,

245 (1973). The District Court made no such determination 

here because Sok did not attempt to make his two suppressionrelated arguments before it.

We have previously held that we can determine “cause” 

for the first time on appeal under Rule 12, so long as there is 

no need to remand the case for an evidentiary hearing. See 

Rose, 538 F.3d at 184. We continue to follow that approach, 

although we recognize that other courts have reached different 

conclusions. See, e.g., Soto, 794 F.3d at 655 (6th Cir.)

(applying plain-error rather than good-cause standard in part 

because the “good-cause standard may be difficult to apply on 

appeal if the issue was not first raised at the district court 

because review for good cause often requires developing and 

analyzing facts”); Acox, 595 F.3d at 732 (7th Cir.) 

(determining that appellate courts cannot determine “good 

cause” under Rule 12 on first impression but may inquire 

whether, if a motion for relief had been made and denied by 

the district court, it would have abused its discretion in doing 

so).
20

See Shotwell Mfg. Co. v. United States, 371 U.S. 341, 363

(1963); Davis v. United States, 411 U.S. 233, 242–44 (1973); 

Wainwright v. Sykes, 433 U.S. 72, 84 (1977); see also Bowline, 

917 F.3d at 1232–34 (discussing Davis and Sykes and requiring 

both cause and prejudice); see also United States v. Mayer, 63 

F.4th 680, 684 (8th Cir. 2023) (requiring cause and prejudice); 

United States v. Santana-Dones, 920 F.3d 70, 81 (1st Cir. 

2019) (same). 

There is a lack of consensus, however, concerning how 

flexible the standard should be. One approach treats it as 

broadly flexible and fact-dependent. See, e.g., United States v. 

Walden, 625 F.3d 961, 965 (6th Cir. 2010) (“Good cause is a 

flexible standard heavily dependent on the facts of the 

particular case as found and weighed by the district court in its 

equitable discretion.”); see also Fed. R. Crim. P. 12, Advisory 

Committee Note to 2014 Amendment (“The party seeking 

relief must show ‘good cause’ for failure to raise a claim by the 

deadline, a flexible standard that requires consideration of all 

interests in the particular case.”); 1A Charles Alan Wright & 

Arthur R. Miller, Federal Practice and Procedure § 194 & 

n.31 (5th ed. West). Another approach construes the exception 

narrowly. United States v. Burke, 633 F.3d 984, 988 (10th Cir. 

2011) (“We rarely, however, grant relief under the good-cause 

exception.”); United States v. Santos Batista, 239 F.3d 16, 19 

(1st Cir. 2001) (describing “good cause” as “single narrow 

exception to the waiver rule”); see also Wright & Miller, 

supra, § 194 & n.32.

We think that “good cause” under Rule 12 is a flexible 

standard that will necessarily depend on the circumstances of 

a particular case. Such treatment accords with the Advisory 

Committee’s advice and the fact that we grant district courts 
21

discretion in determining whether there is good cause to excuse 

untimely Rule 12 arguments. See Fed. R. Crim. P. 12, 

Advisory Committee Note to 2014 Amendment; United States 

v. Desu, 23 F.4th 224, 232 (3d Cir. 2022). 

To direct the application of this flexible standard in our

case, there are some guideposts already in place. Good cause 

may be shown where the information supporting the claim 

arose too late to file a timely Rule 12 motion. See United States 

v. Fattah, 858 F.3d 801, 808 (3d Cir. 2017), as amended (June 

12, 2017) (“late-breaking” evidence supported good cause 

determination); cf. United States v. Pitt, 193 F.3d 751, 760 (3d 

Cir. 1999), as amended (Oct. 15, 1999), and abrogated on 

other grounds by Honeycutt v. United States, 581 U.S. 443

(2017) (concluding there was no good cause shown where 

defendant was “always aware of the facts upon which he” 

based a Rule 12 argument made for the first time on appeal). 

Mere inadvertence of counsel, however, will typically not be

enough to show good cause for raising a Rule 12(b)(3) 

argument for the first time on appeal. See, e.g., United States 

v. Andres, 960 F.3d 1310, 1316 (11th Cir. 2020).

9

 And the 

9 Sok does not make any argument that his trial counsel was 

constitutionally ineffective, so we do not address whether 

ineffective assistance of counsel may constitute “good cause” 

to satisfy Rule 12. We do note, however, that ineffectiveassistance-of-counsel claims should generally be raised 

collaterally. See, e.g., United States v. Jake, 281 F.3d 123, 132 

n.7 (3d Cir. 2002); see also United States v. Taylor, 792 F.2d 

1019, 1025 (11th Cir. 1986) (“We are sympathetic to [the 

defendant’s] argument that a defendant should not be penalized 

for the inadvertence of his or her counsel but are at a loss to see 
22

failure to offer “any colorable explanation” for an untimely 

Rule 12 argument plainly does not suffice to show good cause. 

Rose, 538 F.3d at 184.

As discussed, Sok’s only justification for his failure to 

make his suppression-related arguments before the District 

Court, despite having the opportunity to do so, was his 

counsel’s apparent confusion about the applicable law—i.e., 

the difference between the inevitable-discovery and 

independent-source doctrines. By arguing only that no 

impoundment actually occurred, his counsel inadvertently 

failed to address the Government’s inevitable-discovery 

defense. Instead, his counsel’s argument went to the 

independent-source rule, which was not and is not at issue. 

This mistake is not sufficient to demonstrate good cause. 

Moreover, Sok does not contend that the facts underlying his 

arguments raised for the first time on appeal were not available 

to him to make a timely argument before the District Court. 

Nor does he make any argument that the law at issue was not 

well-established at the time of his counsel’s misunderstanding. 

See Herrold, 962 F.2d at 1140 (describing the difference 

between the inevitable-discovery and independent-source 

doctrines).

Sok encourages us to define “good cause” as 

how we can hold that a district court must entertain a 

suppression motion untimely filed due to inadvertence of 

counsel without completely eviscerating Rule 12(b)(3).”). But 

see United States v. Johnson, 47 F.4th 535, 540 (7th Cir. 2022), 

cert. denied, 143 S. Ct. 813 (2023) (“A claim of ineffective 

assistance of counsel might constitute good cause based on a 

fully developed record.”).
23

contemplating not only justifications going to the timeliness of 

Rule 12(b)(3) arguments—e.g., claiming the facts underlying 

a Rule 12 claim raised for the first time on appeal were not 

previously available—but also a broader range of 

considerations, including exceptional or extraordinary 

circumstances. By this, he points out an exception to forfeiture 

we have typically applied in civil cases10: while we do not 

reach waived arguments, we can reach forfeited issues if there 

are extraordinary or exceptional circumstances counseling us 

to do so. See Dowdell, 70 F.4th at 140; Barna v. Bd. of Sch. 

Dirs. of Panther Valley Sch. Dist., 877 F.3d 136, 147 (3d Cir. 

2017).

11

Even assuming that the good-cause standard under Rule 

10 We have also looked to the extraordinary-circumstances 

exception to forfeiture under direct criminal and collateral 

review where a defendant fails to raise an issue in an opening 

brief. See United States v. Andrews, 681 F.3d 509, 532 (3d Cir. 

2012) (direct); United States v. Albertson, 645 F.3d 191, 195 

(3d Cir. 2011) (direct); United States v. Pelullo, 399 F.3d 197, 

222 (3d Cir. 2005), as amended (Mar. 8, 2005) (collateral). 

11 We have previously stated that we can review untimely

appellate arguments—i.e., arguments raised for the first time 

on appeal or raised on appeal only after an opening appellate 

brief—if there are extraordinary circumstances to do so. See, 

e.g., Brenner v. Loc. 514, United Bhd. of Carpenters & Joiners 

of Am., 927 F.2d 1283, 1298 (3d Cir. 1991); In re Mystic Tank 

Lines Corp., 544 F.3d 524, 528 (3d Cir. 2008); Andrews, 681 

F.3d at 532. Yet we have often described these scenarios in

terms of “waiver.” See Brenner, 927 F.2d at 1298 (“It is well 

established that failure to raise an issue in the district court 
24

12(c)(3) incorporates some or all of the considerations we have 

applied under our exceptional-circumstances jurisprudence, 

Sok has not demonstrated exceptional circumstances here. To 

determine whether they exist, we typically consider any excuse 

for the untimeliness, the extent to which considering the issue 

would prejudice the opposing party, and whether our failure to 

consider it would result in a “miscarriage of justice or 

undermine confidence in the judicial system.” United States v. 

Andrews, 681 F.3d 509, 532 (3d Cir. 2012) (quoting United 

States v. Albertson, 645 F.3d 191, 195 (3d Cir. 2011) (adopting 

these principles)). We have also looked to whether the “public 

interest requires that the new issue be heard on appeal,” United 

States v. Petersen, 622 F.3d 196, 202 n.4 (3d Cir. 2010)

(citation omitted), and whether it involves a pure question of 

law, Barna, 877 F.3d at 147 (“Although our narrow 

exceptional circumstances rule applies to all forfeited issues, 

we have been slightly less reluctant to bar consideration of a 

constitutes a waiver of the argument.” (emphasis added)); 

Pelullo, 399 F.3d at 222 (“It is well settled that an appellant’s 

failure to identify or argue an issue in his opening brief 

constitutes waiver of that issue on appeal.” (emphasis added)). 

But this usage of “waiver” is inconsistent with the waiverforfeiture distinction drawn by the Supreme Court in Olano

and emphasized by our Court in Dowdell. See Olano, 507 U.S. 

at 733; Dowdell, 70 F.4th at 140 (“Although we cannot reach 

waived arguments, appellate courts may resurrect forfeited 

arguments in extraordinary circumstances.” (internal 

quotations and citation omitted)). Instead, absent any 

intentional abandonment, we would now refer to such untimely 

or unpreserved arguments as being forfeited. See Olano, 507 

U.S. at 733.
25

forfeited pure question of law.”).

Again, Sok’s only justification for failing to raise his

arguments against inevitable discovery before the District 

Court is his counsel’s inadvertence. Moreover, reviewing his 

forfeited arguments would prejudice the Government. 

Because it was not put on notice of Sok’s arguments against its 

theory of inevitable discovery before the District Court, the 

Government had no opportunity to develop the record with 

evidence to rebut them. See Rose, 538 F.3d at 182. Nor does 

Sok point to any countervailing public interest.12 

Additionally, refusing to address Sok’s arguments will 

not result in a miscarriage of justice. We have likened the 

miscarriage-of-justice factor to plain-error review. See 

Albertson, 645 F.3d at 196; Andrews, 681 F.3d at 532. Even 

if, for the sake of argument, we apply that standard of review 

here, Sok does not succeed because, at the least, he has not 

shown that any error here was “plain.” See Olano, 507 U.S. at 

734. He points to no governing caselaw resolving the issues 

presented: whether the Government has adequately 

demonstrated that any impoundment of his car for its invalid

12 To the extent Sok argues that an untimely Rule 12 argument 

presenting a purely legal issue—without more—presents 

exceptional circumstances, we disagree. Such a broad-based 

exception would swallow the Rule 12 good-cause standard. 

See Rose, 538 F.3d at 183 n.8 (“[W]e think it unwise to excuse 

a defendant from compliance with Rule 12 even where the 

court of appeals thinks the record is sufficiently developed. To 

do so would ignore the specific language of Rule 12, something 

we do not consider ourselves at liberty to do.”).
26

registration would have been lawful or inevitable. 

On the potential impoundment’s legality, Sok appeals

only to the broad principles underlying the communitycaretaking exception to the Fourth Amendment’s warrant 

requirement. See, e.g., Opperman, 428 U.S. at 368–70; Smith, 

522 F.3d at 313–15. “Th[e] community caretaking 

doctrine . . . is an exception to the warrant requirement of the 

Fourth Amendment and allows police with a non-law 

enforcement purpose to seize or search a person or property ‘in 

order to ensure the safety of the public and/or the individual, 

regardless of any suspected criminal activity.’” Vargas v. City 

of Philadelphia, 783 F.3d 962, 971 (3d Cir. 2015) (quoting 

United States v. King, 990 F.2d 1552, 1560 (10th Cir. 1993)). 

He argues that the Government has failed to show that any 

impoundment under the Live Stop Policy would have served 

the public safety, noting that it has even conceded that the 

“vehicle could have been locked and left at the location of the 

traffic stop while Sok was taken into custody . . . .” App. 209. 

On this basis, he argues that his vehicle’s mere lack of 

registration, without more, is insufficient to allow for 

impoundment under the community-caretaking exception. Yet 

he points to no governing caselaw that clearly supports his 

view. The same goes for his argument that the Government 

failed to show that any impoundment and subsequent inventory 

search would inevitably have occurred.

There being no plain error, we fail to see how a 

miscarriage of justice could result from refusing to reach the 
27

merits of Sok’s arguments.

13

 For these reasons, there are no 

13 While any error was not “plain,” we nonetheless express 

some concern with the Government’s view of the scope of the 

inevitable-discovery doctrine in this case. It is its burden to 

demonstrate, by a preponderance of the evidence, that the 

evidence that the defendant seeks to suppress would have been 

inevitably discovered through lawful means. United States v. 

Vasquez De Reyes, 149 F.3d 192, 195 (3d Cir. 1998); see Nix, 

467 U.S. at 444. The only justification the Government

provides for the legality of impounding Sok’s vehicle is its lack 

of valid registration. It is unclear if this, without more, passes 

muster under the reasonable community-caretaking exception 

to justify the warrantless impoundment of Sok’s vehicle. See 

Opperman, 428 U.S. at 369; Smith, 522 F.3d at 313–15. While 

it is true that, under state law, a car with an expired registration 

cannot be driven, 75 Pa. C.S. §§ 1301, 6309.2(a)(2), the 

Government has not shown that Sok’s car would have needed 

to be moved for any reason. Instead, as discussed, it conceded 

that the vehicle could have been left where it was. Without 

more, invalid vehicle registration might not present a sufficient 

public-safety interest to justify warrantless impoundment. See, 

e.g., United States v. Cervantes, 703 F.3d 1135, 1141 (9th Cir. 

2012) (concluding impoundment of vehicle was not justified 

by community-caretaking exception where there was no 

evidence the vehicle “was parked illegally, posed a safety 

hazard, or was vulnerable to vandalism or theft”); United 

States v. Chavez, 985 F.3d 1234, 1243–45 (10th Cir. 2021)

(refusing to apply the community-caretaking exception to the 

seizure of an unattended firearm from a vehicle where the 

vehicle was lawfully parked and there was little risk someone 

would take the firearm). We also note that the Philadelphia 
28

exceptional circumstances for reaching Sok’s untimely Rule 12 

arguments (again, assuming Rule 12(c)(3)’s good-cause 

standard incorporates our exceptional-circumstances 

jurisprudence).

* * *

We hold that Rule 12(c)(3)’s good-cause standard 

applies to Sok’s suppression-related arguments raised for the 

first time on appeal rather than plain-error review under Rule 

52(b). Because Sok has not demonstrated good cause for his 

failure to raise these arguments before the District Court, we 

cannot consider their merits. Given that his untimely

arguments are the only grounds for his appeal, we affirm the 

judgment of the District Court.

Police Department has since amended the Live Stop Policy in 

a manner that incorporates a public-interest requirement. See 

supra note 1. Nonetheless, while we have concerns with the 

Government’s expansive view of the community-caretaking 

exception in this case, we do not reach the merits for the 

reasons discussed.