In United States v. Aguilera, the 9th Circuit held officers had reasonable suspicion to detain a man who fled after a shots-fired call. Applying the collective-knowledge doctrine, the court ruled the seizure occurred when Aguilera was found hiding, not when he was first ordered to stop. Law enforcement officers should understand how pooled facts support a stop and where that doctrine ends.
United States v. Aguilera, No. 25-3366 (9th Cir. 2026)
Shortly before 0200 hrs, the San Francisco Police Department received two gunshot-detection alerts reporting multiple shots near a bar in the Mission District. Responding officers contacted a witness who said he had seen a Hispanic man wearing a blue jacket fire a gun into the air and walk west on 22nd Street. Another person pointed in the same direction and told officers, “They went that way.”
Officers saw a man walking in that direction. Officer Hurtado confirmed he matched the witness’s description. When officers stopped their patrol vehicle, got out, and ordered the man to stop and get on the ground, he ran. During the pursuit, the man turned toward Officer Hurtado and extended his arm in what the officer believed was a shooting motion. Officer Hurtado momentarily took cover and eventually lost sight of him.
Officer Hurtado broadcast a more complete description: a dark-skinned Hispanic man with long hair wearing a blue jacket, jeans, and black shoes. Another witness told officers the fleeing man had tried to hide beside a parked car and then moved behind a white fence. She confirmed he was still there.
Officer Frisk looked through a gap in the fence and found Fernando Aguilera lying in a narrow strip of weeds. Aguilera was detained at approximately 0208 hrs, about two blocks from where the shots had been detected. Officers found a handgun with a cartridge of the wrong caliber jammed in its chamber, ammunition in a bag Aguilera was carrying, and a magazine in his pocket.
Aguilera moved to suppress the evidence, arguing police lacked reasonable suspicion to detain him. The 9th Circuit disagreed. One important part of the court’s analysis concerned when the Fourth Amendment seizure occurred. Aguilera argued that officers lacked reasonable suspicion when they first ordered him to stop on Mission Street. But he did not stop; he ran.
An officer’s command to stop is not, by itself, a seizure. When an officer makes a show of authority, a seizure ordinarily occurs only when the person submits. (For more on this, see California v. Hodari D., 499 U.S. 621 (1991).) Because Aguilera fled before officers could restrain him, the initial command did not complete a seizure. The court therefore evaluated what officers knew when Aguilera was detained behind the fence — not merely what they knew when they first told him to stop.
By then, officers had considerably more information. They had:
- The gunshot alerts
- A contemporaneous eyewitness account
- Aguilera’s close match to the description, location, and direction of travel
- Aguilera’s flight
- The apparent shooting motion toward Officer Hurtado
- A second witness who saw the fleeing man hide behind the very fence where officers found Aguilera
Flight was not the entire basis for the detention. It was one additional fact in an already substantial collection of facts.
Collective Knowledge Does Not Mean Collective Guessing
The 9th Circuit also relied on the collective-knowledge doctrine, sometimes called the “fellow-officer rule.” The doctrine recognizes that police work is commonly performed by teams. The officer who makes the stop, conducts the search, or places the handcuffs does not necessarily have to know every fact supporting the action.
There are two common applications of the doctrine. First, officers working together in an investigation may combine the facts each has learned, even though every fact has not been expressly communicated to every other officer. There must, however, be some communication or coordination showing that the officers were functioning as a team. Second, an officer or investigative team possessing reasonable suspicion or probable cause may direct another officer to make a stop, search, or arrest. The officer receiving the direction need not be given all the underlying facts. If the originating officer has the required legal basis and communicates an appropriate request, the assisting officer may act on it.
This is where the doctrine is sometimes misunderstood by officers on the street. Collective knowledge does not mean that information known by anyone wearing the same uniform is automatically available to everyone else. Courts cannot search backward through an agency’s files or assemble unrelated pieces of information after the fact to rescue an otherwise unsupported detention. The officers must be cooperating in the investigation, and the facts collectively known to them must establish reasonable suspicion or probable cause before the challenged police action occurs.
Nor does the doctrine create reasonable suspicion where none exists. Ten officers possessing 10 unsupported hunches still possess only hunches. The doctrine permits officers to combine legally significant facts; it does not improve the quality of deficient information.
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Aguilera illustrates the collective knowledge doctrine working as intended. The officers responded to the same gunfire incident, spoke with witnesses, exchanged descriptions and location information, pursued the same suspect, and coordinated the search after he disappeared. The court considered what the participating officers collectively knew when Aguilera was found and detained, rather than artificially limiting the analysis to what Officer Frisk could personally recite at the instant he looked through the fence.
The Takeaway
Officers receiving direction from another officer ordinarily may act without demanding that the entire factual basis be repeated over the radio. But somewhere within the cooperating team, the required reasonable suspicion or probable cause must exist before the seizure or search. Clear broadcasts, accurate descriptions, and careful reports identifying who learned what — and when — remain essential. Collective knowledge is a practical rule for coordinated police work, not a substitute for facts.
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