Whether Henry was arrested when FBI agents stopped his automobile and restricted his freedom of movement.
Holding
Yes. On these facts, the arrest occurred when the agents stopped the car, not when they later announced a formal arrest.
Reasoning
The Government conceded that the arrest occurred when the agents stopped the car, and the Court agreed. Once the agents interrupted Henry and Pierotti and restrained their freedom to leave, the arrest was complete for purposes of this case.
That timing mattered because probable cause must exist when an arrest is made. Evidence uncovered in a later search cannot retroactively validate an arrest that was unsupported when officers first restrained the suspect.