The “Collective Knowledge” Doctrine: When Police Can “Pool” Information to Develop Cause to Stop a Vehicle or Conduct a Search

Today, the Wyoming Supreme Court issued a decision in Guandong v. State, 2022 WY 83, wherein it relied on the so-called “collective knowledge” doctrine to reason that a law enforcement officer was justified in stopping a vehicle as part of a drug trafficking investigation, even in the absence of evidence of a traffic violation. You can read the opinion here:

The “collective knowledge” doctrine “allows an officer to rely on information gathered by other officers” in order to develop the legal justification required to conduct a brief investigatory stop (i.e., a traffic stop) or a search. See Guandong, ¶ 19. That is, “the officer who makes the stop need not have reasonable suspicion that criminal activity is afoot. Instead, the knowledge and reasonable suspicions of one officer can be imputed to another.” United States v. Whitley, 680 F.3d 1227, 1234 (10th Cir. 2012). There are two “types” of collective knowledge: horizontal and vertical. See United States v. Latorre, 893 F.3d 744, 753 (10th Cir. 2018).

The horizontal collective knowledge doctrine can justify a stop or search when “a number of individual officers have pieces of the probable cause or reasonable suspicion puzzle, but no single officer has sufficient information to satisfy the necessary standard.” Whitley, 680 F.3d at 1234 n.3. The inquiry in such a circumstance is “whether the individual officers have communicated the information they possess individually, thereby pooling their collective knowledge” to satisfy the relevant standard. Id. (quoting United States v. Chavez, 534 F.3d 1338, 1345 (10th Cir. 2008)).

The vertical collective knowledge doctrine can justify a stop or search where an officer with reasonable suspicion or probable cause directs another officer to stop a suspect “even without communicating the information justifying the stop.” See Guandong, ¶ 19. Under the vertical collective knowledge doctrine, the key question is whether the original officer actually possessed sufficient information to justify the stop or search.

For example, In United States v. Hensley, 469 U.S. 221 (1985), the Supreme Court held that when officers initiated a Terry stop based on a flyer or bulletin, reliance on the flyer or bulletin was proper so long as the officers that issued the flyer had a reasonable suspicion about the person it targeted.  Id. at 231-32.  Thus, an officer with reasonable suspicion may instruct another officer to make a Terry stop without communicating the basis for the stop, so long as the communicating officer has reasonable suspicion to make the stop himself.

In Guandong, the defendant was stopped by one officer because, earlier in the day, other officers stopped another vehicle and collected evidence that suggested that the defendant was trafficking drugs in his vehicle. See Guandong, ¶¶ 3-12. In particular, the officers who stopped the first car, a Nissan Altima, earlier in the day learned the following pieces of information:

  • the Altima appeared to be traveling with a white Toyota Corolla because “they were going approximately the same speed, made lane changes at the same time, and remained in close proximity to each other”;
  • the driver of the Altima had a pending drug case in Rock Springs, Wyoming;
  • the occupants of the Altima stated they were traveling from Utah, but a “license plate read” showed they came from Sacramento, California;
  • the Altima had an odor of marijuana, but a full vehicle search revealed no marijuana in the car; and
  • the Altima had a spare tire in the trunk from a 2003 Toyota.

The officers let the Altima go. But they did report their findings to a third officer, Trooper Aaron Kirlin.

Trooper Kirlin was familiar with the drug trafficking practice of using a “load vehicle” and a “decoy vehicle” where the two vehicles drove in tandem, but the decoy vehicle’s goal is to attract the attention of law enforcement while the load vehicle drives lawfully/innocuously carrying the illicit cargo. Trooper Kirlin expected that was what was happening here with the Altima and the white Toyota Corolla.

Later in the day, Trooper Kirlin observed the Corolla traveling 59 mph in a 75 mph zone in Albany County. Trooper Kirlin also observed that the car had a single occupant, the male driver, and it had several air fresheners and an ID badge hanging from the rearview mirror.

Trooper Kirlin initiated a traffic stop for two reasons: (1) he suspected the Corolla was transporting drugs based on what he learned from the other officers who stopped the Altima; and (2) he believed the items hanging from the rearview mirror obstructed the driver’s vision in an unlawful or dangerous way. See Guandong, ¶ 10.

Upon stopping the Corolla, Trooper Kirlin informed the driver, Thow Guandong, that he stopped him for the items hanging from the rearview mirror. Trooper Kirlin informed Mr. Guandong that he intended to write Mr. Guandong a warning for this issue and requested Mr. Guandong’s driver’s license, registration, and proof of insurance. Trooper Kirlin had another officer prepare the written warning so that he could run a drug dog around the car. (Mr. Guandong did not challenged the fact of the drug dog sniff or any delays caused by the drug dog sniff.)

The drug dog alerted on the car and the officers found 47 pounds of marijuana and marijuana products in the trunk of the Corolla. See Guandong, ¶ 12. They also noticed that the spare tire was missing. See id.

Mr. Guandong was charged with a host of felony drug offenses. He moved to suppress the drugs on the basis that the initial traffic stop was not justified and violated his federal constitutional rights under the Fourth Amendment to the United States Constitution. Mr. Guandong argued that the items hanging from the rearview mirror did not present sufficient grounds to justify the initial stop. The State responded that Trooper Kirlin had cause to stop Mr. Guandong because of the information he learned about the drug trafficking behaviors and evidence of the Altima and Corolla as well as the obstructed view.

The trial court denied the motion to suppress reasoning that “the initial traffic stop was justified at its inception as a drug trafficking investigation, although not as an obstructed windshield traffic violation.” See Guandong, ¶ 15. Mr. Guandong then entered a conditional guilty plea and was sentenced to 3 to 5 years suspended on 2 years of unsupervised probation. Id. He appealed the denial of his motion to suppress.

The Wyoming Supreme Court affirmed the denial of the motion to suppress on the basis that the “collective knowledge” doctrine gave Trooper Kirlin sufficient grounds to make the initial stop. Chief Justice Fox, writing for the unanimous court, concluded as follows:

“On considering [the] facts in light of his training and experience, Trooper Kirlin concluded that the driver of the Corolla was transporting drugs and, based on the totality of the circumstances, we will defer to his ‘ability to distinguish between innocent and suspicious actions.'” Guandong, ¶ 21 (quoting Feeney v. State, 2009 WY 67,¶ 13, 208 P.3d 50, 54 (Wyo. 2009)).

In so concluding, the Court cited to federal caselaw from the Fifth Circuit Court of Appeals that recognized, “A belief that two vehicles are traveling in tandem in a lead car and load car arrangement may also contribute to a finding of reasonable suspicion.” Id. (citing United States v. Delgado, 99 F. App’x 493, 495 (5th Cir. 2004)).

Bottom line–the officer who stops you may be relying on information supplied to him or her by another officer and yet still have good federal constitutional cause to make the stop. What the Wyoming state constitution says about the lawfulness of this conduct may be different. We just do not know yet. Be wary out there!

(For more coverage of Guandong, check out this recent article in Cowboy State Daily.)


  1. Justice for Cowboys caught my eye. Great article Ryan. Well written and clear. Based on the circumstances it seems the clever officer was justified in his action. The notion of ‘collective knowledge’ has merit. Curious as to how it will become ethically contained in the years to follow.


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