Although the court invalidated use of a checkpoint to run a drug-sniffing K-9, the court's opinion was careful to limit its holding to "ordinary" criminal wrongdoing. The court added, "The Fourth Amendment would almost certainly permit an appropriately tailored roadblock set up to thwart an imminent terrorist attack or to catch a dangerous criminal who is likely to flee by way of a particular route."
The "Search" Issue
Assuming the lawfulness of a detention (stop is based on a reasonable suspicion of criminal activity), merely running the K-9 around the vehicle or container does not constitute a Fourth Amendment "search," and need not be independently justified. Even while invalidating the Indianapolis drug checkpoint in the Edmond case based on the illegal seizure, the court noted that the K-9 sniff was not itself a search: "The fact that officers walk a narcotics detection dog around the exterior of each car does not transform the seizure into a search." (Indianapolis v. Edmond)
In U.S. v. Place, DEA agents at a New York airport, acting on information from officials at the Miami airport, seized Raymond Place's luggage and held it for 90 minutes before a K-9 was brought to sniff it. After the dog alerted, agents opened the luggage and discovered a large quantity of cocaine. The Supreme Court suppressed the cocaine as evidence because it held that the 90-minute detention of the luggage was too long, but the court noted that the dog sniff did not constitute a search:
"The sniff discloses only the presence or absence of narcotics, a contraband item. Therefore, we conclude that the particular course of investigation that the agents intended to pursue here-exposure of respondent's luggage, which was located in a public place, to a trained canine-did not constitute a 'search' within the meaning of the Fourth Amendment" (U.S. v. Place).
In Illinois v. Caballes, a state trooper stopped a car for speeding. During the time it would normally take to issue a traffic warning or citation, another officer arrived with a K-9, ran it around the car, and searched the trunk after the dog alerted there. Driver Caballes moved to suppress the marijuana found in his trunk, but the Supreme Court denied the motion. Since in this case the seizure of the suspect was justified by the traffic violation, and since a K-9 sniff is not a search, there were no grounds for suppression.
Said the court:
"Official conduct that does not compromise any legitimate interest in privacy is not a search subject to the Fourth Amendment. We have held that any interest in possessing contraband cannot be deemed 'legitimate,' and thus any governmental conduct that only reveals the possession of contraband compromises no legitimate privacy interest. The trial judge found that the dog sniff was sufficiently reliable to establish probable cause to conduct a full-blown search of the trunk. Accordingly, the use of a well-trained narcotics detection dog during a lawful traffic stop does not implicate legitimate privacy interests" (Illinois v. Caballes).
Combining Legal Principles
In Whren v. U.S. and Arkansas v. Sullivan, the Supreme Court ruled that a lawful traffic stop could be used to provide the opportunity for a brief narcotics investigation. In Caballes, the court said that a K-9 could be run during a valid traffic stop. This means that if you have a K-9 ready, you may stop suspected drug offenders for moving or equipment violations and run the dog while you discuss the traffic violation. If the dog hits, you have PC to search and arrest.
Federal appeals courts have approved of such tactics as setting up narcotics checkpoint signs (without any actual checkpoint) and stopping cars when they commit traffic violations while trying to avoid the advertised checkpoint. The traffic stop is permissible under Whren, and a K-9 sniff within the scope of such stops is permissible under Caballes (U.S. v. Wright — stop sign violation; U.S. v. Adler — improper signal).