The Collective Knowledge Doctrine

In certain situations, a police officer may be directed by a colleague and/or supervisor to make an arrest for a crime that the officer did not personally observe. The officer may feel as if they’re in a precarious situation, particularly when the directing officer is their supervisor. In this situation, the officer may believe that their supervisor is essentially directing them to violate the purported suspect’s rights under the Fourth Amendment. After all, before making an arrest, doesn’t the arresting officer need probable cause to do so?

The Case

United States v. Williams4 illustrates how the collective knowledge doctrine can apply. In the summer of 2008, a Drug Enforcement Agency (DEA) task force was conducting an investigation of a purported drug-trafficking organization. The investigation used court-authorized wiretaps to intercept phone calls between individuals suspected to be involved in the drug ring.

On July 15, 2008, the DEA intercepted phone calls made between three individuals discussing “car parts” arriving at “the shop” located at the 2700 block of North Monitor Avenue.5 DEA agents conducted surveillance on the house and stopped one of the three individuals, who admitted to purchasing two kilograms of cocaine at the Monitor Avenue residence from the other two individuals involved in the prior telephone communications.

The following day, DEA agents intercepted additional phone calls between the two individuals identified by the person they’d stopped the day before. These two individuals discussed meeting a “black guy” at the “shop on Monitor” later that day.6 The agents decided to conduct surveillance on the Monitor Avenue residence at the anticipated time of the transaction. The agents also decided that they would put officers from the Chicago Police Department (CPD) on standby to assist.

A CPD officer, who was also a member of the DEA task force, acted as a liaison officer and coordinated the efforts between the DEA and the CPD. The liaison officer met with several CPD officers to brief them of the anticipated transaction. Even though he had not personally heard the intercepted communications, he was in contact with the DEA agents who had. He advised them that an individual would be coming to the residence to purchase drugs and wanted the officers to position themselves at various locations in the area. He advised the CDP officers that he would provide them with information about the suspect vehicle and that they should stop the vehicle after developing their own probable cause to do so.7

At approximately 11:30 a.m. that day, a Chevy Suburban occupied by Williams and another individual parked in an alley behind the Monitor Avenue residence and entered the backyard. Williams was carrying a brown shoebox. Fifteen minutes later, the two individuals exited the house carrying the same brown shoe box and left in the Suburban. The liaison officer, who observed these activities, called a CPD officer, gave him the description of the vehicle and the license plate, and informed him of the vehicle’s direction of travel.

The CPD officer and his partner eventually stopped the Suburban. After instructing the two occupants out of the car and conducting a pat-down search, they found marijuana in Williams’ pocket. A search of the Suburban led to the discovery of a brown shoebox containing a brick of cocaine.

Williams was charged with one count of possession with the intent to distribute 500 grams or more of cocaine in violation of 21 U.S.C. Section 841(a)(1). Williams filed a motion to suppress the evidence seized by the police as a result of the traffic stop.

At the hearing, the CPD officer who conducted the traffic stop testified that after following the Suburban, he pulled up alongside and observed that the passenger wasn’t wearing his seatbelt.8 He conducted a traffic stop based on that violation alone. The officer testified that he was aware that the seatbelt violation would not justify a search of the vehicle or its occupants; however, when he approached the car, he noticed “crumbs” of marijuana on the center console and two cigar-type objects in an open ashtray. Because he observed what he believed to be marijuana, he ordered the occupants out of the Suburban.

Williams, on the other hand, testified that although there were two marijuana cigars in the ashtray, he had closed the ashtray when he pulled over. He also claimed that there were no “crumbs” on the center console.

The Determination

The district court found that the officer’s testimony was not credible, relying on the officer’s manner of testifying and the officer’s claimed strategy for effecting the search of the vehicle, which the court felt made “little sense.”9 The district court questioned why the officer would pull over the vehicle for a violation he knew would not provide him with the probable cause that he needed to search the vehicle. It also did not believe the officer casually observed marijuana in plain view in a vehicle that Williams and his passenger knew contained a kilogram of cocaine in a shoebox in the back seat.

As such, the district court found that the search of the vehicle was not supported by the seatbelt violation or the purported marijuana in plain view. Even so, the district court still denied Williams’ motion to suppress, finding that the DEA’s investigation (wiretaps and surveillance) gave the CPD officer probable cause to search the vehicle under the collective knowledge doctrine.

Williams entered into a conditional guilty plea, which allowed him to appeal the district court’s motion to suppress ruling.

On appeal, the court addressed two issues: whether the DEA task force had probable cause to search the vehicle and, if so, whether that information could be imputed to the officers who eventually conducted the traffic stop and search under the collective knowledge doctrine.

The appellate court concluded that the facts known to the DEA task force easily supported a search of the vehicle because “taken as a whole, [the] facts justified the agents’ belief that Howard and Williams purchased drugs at the Monitor residence, and that a search of the Suburban would uncover those drugs.”10 It also found that the “search was supported by probable cause because the DEA’s collective knowledge could be imputed to the officers under the collective knowledge doctrine.”11

However, Williams argued that if the collective doctrine applied, only the liaison officer’s knowledge, not that of the entire DEA task force, could be imputed to the CPD officer conducting the traffic stop. Williams based his argument on two reasons: First, he claimed that the knowledge learned from the wiretaps couldn’t be imputed to the officer conducting the traffic stop because the liaison officer did not listen to the wiretapped conversations. Second, he claimed that the DEA agents’ knowledge couldn’t be imputed to the liaison officer because the liaison officer worked for a different agency, the CPD.

The court of appeals found that although the liaison officer was a CPD officer, he was a member of the DEA task force. As such, he became aware of the intercepted calls suggesting that a narcotics sale would occur at the Monitor Avenue residence. He was also in radio contact with other members of the task force surveillance team, who informed him of Williams leaving the residence with a shoe box. Therefore, the liaison officer had indirect knowledge of the facts supporting the probable cause.

The appellate court further stated that it was of no import that the knowledge was indirect because it was a situation in which the officers were part of a coordinated investigation and were in communication with one another. The knowledge of a team of officers “working closely in monitoring a drug transaction as it unfolds may be mutually imputed” even in the absence of “express testimony that the specific or detailed information creating the justification for the stop was conveyed.”12

With respect to Williams’ second contention—that the liaison officer was actually employed by the CPD and not the DEA and, therefore, the collective knowledge doctrine couldn’t be imputed to him—the court of appeals stated that the language of some of its precedents was misleading. For example, the court of appeals had stated in prior decisions that “knowledge may be imputed to an officer ‘so long as the knowledge of the officer directing the [challenged action], or the collective knowledge of the agency he works for, is sufficient to constitute probable cause.’”13

According to the Court of Appeals, “that language was designed to recognize that the knowledge of other officers may be imputed to the requesting officer, so long as the officers are in close communication with one another.”14 In this case, the liaison officer was a member of the DEA task force and worked closely with the DEA agents in this investigation. Simply because he carried a badge issued by the CPD and not the DEA, the court found, did not preclude the application of the collective knowledge doctrine.

In Sum

This scenario is an excellent example of why it’s so important that police reports be well written by officers involved in a particular investigation or task. By that, I don’t mean that the CPD officer should be required to write what the other officers knew when they passed information on to him—indeed, that would not be proper. On the other hand, the DEA agents should document the information they learned from the court-approved wiretaps and surveillance. The liaison officer should document what information he learned from the DEA agents and when he learned of that information. Finally, the CPD officer should write, in a separate report, what he learned, when he learned it and from whom he heard it.

Together, the reports should demonstrate a seamless flow of information that supports the application of the collective knowledge doctrine.          

Collective Knowledge Doctrine

The collective knowledge doctrine permits a police officer to stop, search or arrest a suspect at the direction of another police officer or police agency, even if the officer doesn’t have any firsthand knowledge of the facts that amount to the level of suspicion to permit the given action.1 In other words, that officer doesn’t violate the suspect’s rights under the Fourth Amendment if the knowledge of the officer directing the stop, search or arrest is sufficient to constitute probable cause.2

According to the Seventh Circuit Court of Appeals, the collective knowledge doctrine is applicable where the following three elements are met:

1. The officer taking the action must act in objective reliance on the information received;

2. The officer providing the information (or the agency for which they work) must have facts supporting the level of suspicion required; and

3. The stop must be no more intrusive than would have been permissible for the officer requesting it.3

Although the phrase “collective knowledge doctrine” may not be immediately acknowledgeable by police officers, the practice itself is widely recognized.


  1. See, United States v. Hensley, 469 U.S. 221, 232-33 (1985).

  2. United States v. Harris, 585 F.3d 394, 400 (7th Cir. 2009).

  3. United States v. Nafzger, 974 F.2d 906, 911 (7th Cir. 1992).

  4. 627 F.3d 247 (7th Cir. 2010).

  5. Id. at 249.

  6. Id.

  7. Id.

  8. In Illinois, drivers and most passengers must wear seatbelts; however, police officers are not permitted to search or inspect a motor vehicle, its contents, the driver or a passenger solely because of a driver or passenger’s failure to wear a seat belt. 625 ILCS 5/12-603.1(a) and (f).

  9. Id. at 250.

10. Id. at 251-52.

11. Id. at 253.

12. Id. at 255 (citations and internal quotations omitted).

13. Id. (citation omitted).

14. Id.


Do not construe this column as legal advice. Each police officer should consult with an attorney in their jurisdiction for legal advice on any specific issue.


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