Certified Canine “Alert” (Without a Full “Indication”) Can Supply Probable Cause Under the Totality of the Circumstances

1. Introduction

In United States v. Conchas-Mancilla (5th Cir. Apr. 16, 2026), the Fifth Circuit considered whether Border Patrol agents had probable cause to search a vehicle at a routine immigration checkpoint after a certified drug-detection dog exhibited an alert but did not perform a trained final indication (e.g., sit/scratch).

The defendant, Jesus Arturo Conchas-Mancilla, sought suppression of cocaine discovered in a hidden bumper compartment, arguing the dog’s behavior was insufficient to justify a warrantless search. The Government responded that the dog’s reliable alerts, viewed under the totality of the circumstances, established probable cause.

The key legal issue: Can a certified dog’s “alert,” without a full “indication,” provide probable cause to search a vehicle?

2. Summary of the Opinion

The Fifth Circuit affirmed denial of the motion to suppress. Applying the Supreme Court’s totality-of-the-circumstances framework, the court held that the dog’s repeated, strong alerts—combined with extensive evidence of the dog’s training, certification, and performance—would lead a reasonably prudent person to believe the search would reveal contraband.

The court rejected the defendant’s attempt to treat “indication” as categorically necessary for probable cause, explaining that Fifth Circuit and Supreme Court precedent do not impose rigid signaling requirements on detection dogs.

3. Analysis

A. Precedents Cited

United States v. Alvarez, 40 F.4th 339 (5th Cir. 2022)
Cited for the suppression-review framework: factual findings reviewed for clear error, legal conclusions de novo, and evidence viewed in the light most favorable to the Government as the prevailing party. This framing mattered because the district court credited agents’ live testimony that the dog alerted and was reliable—findings insulated by deferential review.
United States v. Zavala, 541 F.3d 562 (5th Cir. 2008)
Used to classify probable cause as a legal conclusion (reviewed de novo). Even so, the building blocks of that conclusion—whether the dog alerted and whether the dog was reliable—were treated as factual findings.
United States v. Outlaw, 319 F.3d 701 (5th Cir. 2003)
Cited for the proposition that whether a canine alerted and canine reliability are factual findings. This supported deference to the district court’s credibility determinations about what the dog did and what it meant.
United States v. Gibbs, 421 F.3d 352 (5th Cir. 2005) (quoting United States v. Santiago, 410 F.3d 193 (5th Cir. 2005))
Reinforced that clear-error review is “particularly strong” when the district court’s ruling rests on live oral testimony—central here because the suppression hearing spanned two days and relied heavily on witness demeanor and expert interpretation of canine behavior.
United States v. Keller, 123 F.4th 264 (5th Cir. 2024)
Provided the opinion’s vocabulary distinguishing Border Patrol terms “alert” (instinctual posture change upon odor encounter) and “indication” (trained final response). The defendant leaned on Keller to argue that only an indication is sufficient “by itself.” The panel read Keller as consistent with a flexible totality inquiry and as not holding that alerts are categorically insufficient.
United States v. Clayton, 374 F. App'x 497 (5th Cir. 2010)
Directly supported the court’s rejection of rigid canine signaling rules: Fourth Amendment doctrine does not require a “specific and consistent code” for drug dogs. This undermined the defense’s attempt to turn “indication” into a necessary formal requirement.
Florida v. Harris, 568 U.S. 237 (2013)
The centerpiece precedent. The Fifth Circuit invoked Harris for (1) the totality-of-the-circumstances test for probable cause from a dog alert, (2) the “lens of common sense,” and (3) the principle that courts may presume probable cause from an alert by a dog certified/tested by a “bona fide organization,” subject to conflicting evidence. The panel also emphasized that Harris did not “split hairs” between alert and indication.
United States v. Martinez, 102 F.4th 677 (5th Cir. 2024);
United States v. Shen, 749 F. App'x 256 (5th Cir. 2018);
United States v. Clayton, 374 F. App'x 497 (5th Cir. 2010)
Cited collectively for the Fifth Circuit’s repeated holdings that an alert short of a full indication can still establish probable cause under the totality of the circumstances. Shen was particularly on-point in rejecting any requirement that a dog reach a “full and final alert” before probable cause exists.
United States v. Sanchez-Pena, 336 F.3d 431 (5th Cir. 2003)
Used to confirm the companion proposition: an indication by a drug dog is routinely treated as providing probable cause. The panel positioned indications as “near-dispositive” evidence—without making them exclusive.
United States v. Villafranco-Elizondo, 897 F.3d 635 (5th Cir. 2018)
Cited to show the court’s broader reluctance to impose rigid dog-sniff rules (there, rejecting the idea that a failure to alert negates existing probable cause). It supported the panel’s theme that canine behavior is evaluated contextually, not mechanistically.

B. Legal Reasoning

The panel’s reasoning proceeded in three linked steps:

Clarify the doctrinal test: The court reaffirmed that probable cause from canine activity is assessed under the totality of the circumstances (from Florida v. Harris), not by a bright-line requirement that a dog perform one particular trained “indication.”
Reject an “indication-only” rule: The defendant’s interpretation of a footnote in United States v. Keller was not adopted. The panel treated Keller as consistent with Harris: indications may be extremely strong evidence, but alerts can also suffice depending on context. The opinion also emphasized Fifth Circuit precedent (e.g., United States v. Shen, United States v. Martinez) permitting probable cause based on alerts.
Apply the totality test to the record: The district court found (and the panel upheld under clear-error review) that (a) the dog alerted strongly and repeatedly at the rear bumper area, and (b) the dog was highly reliable, having been certified by U.S. Customs and Border Protection, never requiring remedial training, and achieving notable performance results. With those facts, common sense supported probable cause that the vehicle contained contraband.

Notably, the court treated the dog’s certification by U.S. Customs and Border Patrol as satisfying Harris’s “bona fide organization” concept, enabling a presumption of probable cause absent meaningful contrary evidence.

C. Impact

Practically, United States v. Conchas-Mancilla strengthens (and clarifies) Fifth Circuit law in three ways:

No categorical “indication” requirement: Litigants cannot successfully argue, merely as a definitional matter, that an alert is constitutionally insufficient unless followed by a trained final indication.
Record-building becomes decisive: Because alert/reliability are factual findings reviewed for clear error, suppression outcomes will often turn on hearing testimony, handler credibility, training records, and expert interpretation of the dog’s behavior.
Certification + observed behavior can carry the day: The combination of bona fide certification (per Harris) and specific, described alert behaviors (e.g., posture change, pulling, focused interest, frustration behaviors) will frequently suffice for probable cause—especially where the alert is repeated and localized to a particular vehicle area.

For future cases, the decision encourages courts to focus less on semantics (“alert” vs. “indication”) and more on whether the dog’s behavior, training, and reliability would lead a reasonable officer to expect contraband will be found.

4. Complex Concepts Simplified

Probable cause: A practical, common-sense standard: whether there is a fair probability that evidence of a crime or contraband will be found in a particular place. It does not require certainty.
Alert vs. indication: Per United States v. Keller, an alert is an instinctual, first-recognition change in posture/behavior when the dog encounters a trained odor; an indication is a trained final response (like sitting or scratching) after detection. This case holds that an alert can still support probable cause when assessed under the totality of the circumstances.
Totality of the circumstances: From Florida v. Harris: courts evaluate all relevant facts together (training, certification, handler observations, dog’s behavior, context) rather than applying a single mechanical rule.
Clear error vs. de novo review: Appellate courts largely defer to trial courts on factual determinations (clear error), especially when based on live testimony (per United States v. Gibbs and United States v. Santiago), but independently review legal conclusions like whether those facts amount to probable cause.

5. Conclusion

United States v. Conchas-Mancilla reaffirms a flexible Fourth Amendment rule: within the Fifth Circuit, a certified drug dog’s alert—even absent a trained final indication—can establish probable cause when the totality of the circumstances shows reliability and a meaningful, localized reaction to the odor of contraband. The decision situates Fifth Circuit doctrine squarely within Florida v. Harris’s common-sense framework and discourages bright-line challenges based solely on canine nomenclature.