Ex Parte Buccal-Swab DNA Warrants: No Pre-Issuance Hearing Required, and Probable Cause Need Not Identify a Viable Comparison Sample

1. Introduction

United States v. Leeper (2d Cir. Aug. 13, 2026) addresses two recurring Fourth Amendment flashpoints in modern investigations: (i) when the government may obtain a suspect’s DNA by buccal swab via warrant, and whether the warrant application must identify an existing, usable DNA comparison sample; and (ii) when officers may hold/impound a vehicle under the community-caretaking rationale, thereby triggering an inventory search.

Defendant-Appellant Kyle M. Leeper pleaded guilty to (1) intentional murder while engaged in a controlled substance offense (21 U.S.C. § 848(e)(1)(A)), (2) methamphetamine conspiracy (21 U.S.C. §§ 841 & 846), and (3) felon-in-possession (18 U.S.C. § 922(g)(1)), while reserving the right to appeal the denial of suppression motions. He challenged (a) evidence seized from a pickup truck after it was held and inventory-searched, and (b) evidence obtained from a buccal-swab DNA warrant issued ex parte.

The Second Circuit affirmed. Judge Sullivan concurred in the judgment, emphasizing that Mathews v. Eldridge is inapplicable to search warrants because the Fourth Amendment supplies the “process that is due.”

2. Summary of the Opinion

  • Probable cause for DNA warrant: The court held that the warrant application established probable cause to collect Leeper’s DNA even though it did not identify a specific “viable DNA sample” already available for comparison. Probable cause is a probability-based, fact-specific inquiry, and the affidavit’s description of extensive physical evidence tied to the homicide supported a “fair probability” that DNA comparison evidence could be developed.
  • Ex parte DNA warrant procedure: Leeper had no constitutional right to notice and an opportunity to be heard before issuance of the buccal-swab warrant. Even assuming Mathews v. Eldridge applied, the government’s interests in investigative confidentiality and efficacy outweighed the private interest and the incremental value of added pre-deprivation procedures.
  • Vehicle hold/impound: Holding the vehicle was reasonable under the Fourth Amendment’s community-caretaking doctrine where the truck lacked valid registration and neither occupant could lawfully drive it away, even though it was parked in a commercial lot.

3. Analysis

A. Precedents Cited

1) Probable cause framework (DNA warrant)

The court grounded its probable-cause analysis in canonical Supreme Court and Second Circuit authorities:

  • Illinois v. Gates, 462 U.S. 213 (1983): supplies the “practical, common-sense” totality-of-the-circumstances test and the “fair probability” standard. Leeper is an application of Gates to a DNA-collection warrant.
  • United States v. Raymonda, 780 F.3d 105 (2d Cir. 2015): reinforces deference to the issuing judge and rejects bright-line rules in probable cause (“fluid concept”). The panel uses Raymonda to reject Leeper’s requested categorical rule that probable cause fails unless comparison DNA is identified.
  • United States v. Leon, 468 U.S. 897 (1984): invoked for the proposition that reasonable minds may differ on probable cause and reviewing courts should not treat probable cause review as de novo.
  • Walczyk v. Rio, 496 F.3d 139 (2d Cir. 2007): emphasizes that probable cause concerns probabilities, not “hard certainties.” This directly answers Leeper’s claim that the affidavit must establish certainty that usable comparison DNA exists.

The opinion also acknowledged a split among lower courts on whether a DNA-collection warrant must show that recovered evidence has yielded a usable DNA profile, citing cases including United States v. Marshall, United States v. Pakala, United States v. Robinson, United States v. Jennings (more demanding), contrasted with United States v. Harrison, United States v. Sedillo, United States v. Burkhalter, and In re Search Warrant (more permissive). The Second Circuit did not adopt either camp categorically; instead, it announced a fact-sensitive approach consistent with Gates/Raymonda.

2) Ex parte warrants, due process, and the Fourth Amendment

On procedure, the panel relied heavily on Supreme Court descriptions of warrant practice:

  • Franks v. Delaware, 438 U.S. 154 (1978): states that the “pre-search proceeding is necessarily ex parte,” because notice could enable destruction or removal of evidence. Leeper extends this logic to DNA warrants, emphasizing investigative confidentiality beyond simple “spoliation of DNA.”
  • United States v. U.S. Dist. Ct. for E. Dist. of Mich., S. Div., 407 U.S. 297 (1972): highlights that warrant applications involve “no public or adversary proceedings.”
  • Gerstein v. Pugh, 420 U.S. 103 (1975): provides the doctrinal anchor for Judge Sullivan’s concurrence and informs the majority’s skepticism: the Fourth Amendment’s balance generally defines “process that is due” in criminal searches and seizures.
  • United States v. Grubbs, 547 U.S. 90 (2006): underscores that the Constitution protects through ex ante judicial probable-cause review and ex post suppression remedies, not by allowing targets to litigate warrant bases pre-execution.

The majority discussed Mathews v. Eldridge, 424 U.S. 319 (1976), largely because Leeper framed his argument in procedural due process terms. It also cited Second Circuit cases applying Mathews in adjacent contexts: United States v. Abuhamra (bail pending appeal, distinguishing warrants) and Krimstock v. Kelly (post-seizure vehicle retention), while recognizing that “no federal appellate court” had applied Mathews to warrant issuance. Judge Sullivan’s concurrence argued the court should have held Mathews categorically inapplicable, relying on Gerstein v. Pugh, and warning (with reference to Medina v. California and Hines v. Miller) against importing civil due-process balancing into criminal procedure governed by specific Bill of Rights provisions.

3) DNA privacy and bodily intrusion

  • Maryland v. King, 569 U.S. 435 (2013): used to characterize buccal swabs as “negligible” physical intrusions (“gentle process”).
  • Nicholas v. Goord, 430 F.3d 652 (2d Cir. 2005), and Roe v. Marcotte, 193 F.3d 72 (2d Cir. 1999): support the notion that statutory safeguards limiting DNA use, disclosure, and expungement reduce privacy concerns in the database context.
  • Riley v. California, 573 U.S. 373 (2014): invoked analogically to show that many warrants (e.g., for cellphones) expose vast intimate data, yet are still obtained ex parte—undercutting Leeper’s attempt to treat DNA as uniquely requiring pre-issuance adversarial process.

4) Vehicle holding/impoundment and community caretaking

  • United States v. Lyle, 919 F.3d 716 (2d Cir. 2019): provides the governing Second Circuit framework for assessing reasonableness of impoundment (first step) and inventory search (second step). Leeper, like Lyle, addresses only the impoundment/holding decision.
  • United States v. Lopez, 547 F.3d 364 (2d Cir. 2008): confirms reasonableness of impoundment when arrest or incapacity leaves no lawful driver to remove the vehicle.

B. Legal Reasoning

1) New clarification on DNA-warrant probable cause

The court treated Leeper’s core submission as a proposed categorical rule: without identified, viable comparison DNA, a buccal-swab warrant lacks probable cause because the suspect’s DNA “alone” is “useless.” The panel rejected that as inconsistent with the nature of probable cause under Illinois v. Gates and United States v. Raymonda.

The opinion’s operative principle is functional: probable cause for obtaining a suspect’s DNA depends on the totality—such as whether there is physical evidence that could plausibly bear DNA (e.g., zip ties used to bind the victim, a rental car, the body, casings/projectiles), and whether the suspect plausibly contacted those items. The affidavit need not prove that evidence has already yielded a usable profile; it must show a “fair probability” that collecting the suspect’s DNA will produce evidence of crime. By highlighting the “plethora of physical evidence” and Leeper’s “ample opportunity to deposit touch DNA,” the panel found a substantial basis for the issuing judge’s determination.

2) Ex parte DNA warrants and procedural due process

The majority approached the due-process claim conservatively: it expressed “serious doubts” about applying Mathews v. Eldridge to search warrants (given Gerstein v. Pugh and the Fourth Amendment’s tailored protections), but proceeded to hold that even if Mathews applies, it does not require pre-issuance notice and a hearing for buccal-swab DNA warrants.

The key move is rejecting Leeper’s premise that ex parte warrants are justified only to prevent spoliation of the thing sought (here, DNA). The court broadened the government’s interest to include preserving the confidentiality of an ongoing investigation—protecting witnesses, preventing obstruction, avoiding premature disclosure of investigative theories, and preventing flight by the target or co-conspirators. The court stressed that pre-issuance notice would likely entail disclosure of the warrant application itself, which can function as a “roadmap” of the government’s evidence and theory.

The court also highlighted practical burdens and delays inherent in pre-deprivation adversarial process (time to retain counsel, briefing, hearings), invoking the Supreme Court’s recognition in Gilbert v. Homar and Parratt v. Taylor that post-deprivation process can suffice where quick action is needed or pre-deprivation process is impractical.

On the private-interest side, the court acknowledged DNA’s sensitivity but treated the actual bodily intrusion as minimal under Maryland v. King and noted statutory controls on DNA disclosure and expungement (citing federal statutory safeguards and parallel state safeguards). It further reasoned that adopting a “DNA-is-special” pre-issuance hearing rule would destabilize warrant practice for other similarly privacy-revealing searches, especially digital searches post-Riley v. California.

On the risk-of-error factor, the court emphasized existing safeguards: neutral judicial review for probable cause and ex post remedies, including suppression under the exclusionary rule—consistent with United States v. Grubbs.

3) Reasonableness of holding the vehicle

Applying United States v. Lyle and the community-caretaking doctrine, the panel framed the relevant question narrowly: whether the hold/impound was objectively reasonable, not whether the ensuing inventory search complied with policy (which Leeper did not challenge on appeal).

The decisive facts were (i) expired registration (no lawful operation), and (ii) neither occupant had a valid license. Even though the vehicle was in a commercial lot rather than on a public street, the court treated location as one factor in a totality analysis and found it reasonable to prevent the vehicle from becoming a nuisance, being stolen/damaged, or remaining unlawfully situated for an indeterminate period. The panel also reiterated Lyle’s point that strict compliance with standardized impoundment procedures, while helpful, is not a constitutional prerequisite.

C. Impact

1) DNA warrants: Leeper is a meaningful Second Circuit precedent because it rejects a bright-line requirement that the government identify an existing “viable” comparison DNA sample before obtaining a suspect’s DNA by warrant. This is likely to influence magistrates and district courts confronting the cited lower-court split and will generally make DNA warrants easier to sustain where the affidavit ties the suspect to physical instrumentalities plausibly bearing DNA.

2) Ex parte process for DNA collection: The decision strongly reinforces the orthodox understanding—rooted in Franks v. Delaware—that warrant proceedings are ex parte and that “DNA sensitivity” does not itself constitutionalize a pre-issuance adversarial hearing. The concurrence adds an additional signal: future panels may hold categorically that Mathews balancing does not apply to warrants at all, aligning the doctrine more explicitly with Gerstein v. Pugh.

3) Vehicle holds in private lots: The opinion confirms that community-caretaking impoundment can be reasonable even off public streets, particularly where legal operation is impossible (expired registration, unlicensed drivers). It also continues the Second Circuit’s trend in United States v. Lyle of resisting rigid “standardized procedures” constitutional requirements for impoundment decisions.

4. Complex Concepts Simplified

  • Probable cause: Not proof beyond a reasonable doubt. It is a practical judgment that there is a “fair probability” evidence will be found, assessed under the “totality of the circumstances” (Illinois v. Gates).
  • Ex parte warrant: A request made to a judge without notifying the target. Warrant practice is traditionally ex parte to avoid compromising investigations (Franks v. Delaware; United States v. U.S. Dist. Ct. for E. Dist. of Mich., S. Div.).
  • Buccal swab: A cheek swab used to collect saliva cells for DNA; treated as a minimal physical intrusion (Maryland v. King).
  • “Touch DNA”: DNA that can be left on objects through skin contact (e.g., bindings, vehicle surfaces). Its possible presence supports the probability logic underlying probable cause.
  • Procedural due process / Mathews v. Eldridge: A civil-law framework balancing private interest, risk of error, and government interest to decide what procedures (like hearings) are required. Leeper holds that even if applied, it does not mandate pre-warrant hearings for buccal-swab DNA.
  • Community caretaking (vehicles): Police authority to remove vehicles for public safety and administrative reasons, not as a pretext to investigate crime. The question is objective reasonableness under all the circumstances (United States v. Lyle).
  • Inventory search: A standardized administrative search of an impounded/held vehicle to document property and protect against claims. Leeper’s appeal focused on the reasonableness of the hold, not the inventory-search mechanics.
  • Exclusionary rule: A post-search remedy—if police violate the Fourth Amendment, evidence can be suppressed to deter future violations (discussed alongside United States v. Grubbs and the opinion’s risk-of-error analysis).

5. Conclusion

United States v. Leeper clarifies that probable cause to seize a suspect’s DNA by buccal-swab warrant does not categorically require identification of an already-confirmed viable comparison sample; probable cause remains a totality-based probability inquiry. It also reaffirms the constitutional legitimacy of ex parte warrant proceedings for DNA collection during ongoing investigations, rejecting the claim that due process requires pre-issuance notice and a hearing. Finally, it strengthens Second Circuit vehicle-impoundment doctrine by holding that a vehicle may be reasonably held under community caretaking even from a private commercial lot when no lawful driver and no valid registration exist.