Whether the Fourth Amendment permits a warrantless public arrest for a felony when officers have probable cause but had time to obtain an arrest warrant.
Holding
Yes. A duly authorized officer may make a warrantless public felony arrest on probable cause; the Fourth Amendment does not additionally require exigent circumstances or proof that obtaining a warrant was impracticable.
Reasoning
The postal inspector acted under a federal statute and regulation authorizing Postal Service officers to make warrantless felony arrests when they have reasonable grounds, or probable cause, to believe a federal felony has been committed. The courts below accepted that the reliable informant's information established probable cause that Watson possessed stolen mail, so the arrest complied with the governing federal law.
Congress's authorization carried substantial weight because the Fourth Amendment asks whether a seizure is unreasonable. Congress had likewise long authorized warrantless felony arrests by marshals, FBI agents, and other federal officers. The Court declined to hold that this longstanding legislative judgment was facially unreasonable.
The Court's precedents had consistently treated probable cause, rather than an arrest warrant, as the constitutional touchstone for warrantless felony arrests. Cases such as Carroll, Draper, Ker, Henry, and Gerstein reflected the settled rule that an officer may arrest for a felony without a warrant when probable cause exists. Gerstein specifically observed that the Court had never invalidated a probable-cause arrest solely because officers did not obtain a warrant.
History supported the same result. At common law, peace officers could arrest without a warrant for felonies on reasonable grounds, including felonies not committed in their presence. That rule was broadly accepted in the States, and the early Congress gave federal marshals the arrest powers held by state sheriffs shortly after the Fourth Amendment was adopted.
The Court acknowledged that officers may wisely obtain an arrest warrant when practicable, both to secure a neutral probable-cause determination and to strengthen the prosecution's position. But that practical preference could not become a constitutional rule requiring courts to conduct after-the-fact litigation over whether a warrant was feasible or whether exigent circumstances existed. The Court limited its ruling to Watson's public arrest and did not decide when a warrant is required to enter a private place to make an arrest.