The Supreme Court affirmed Wednesday that police have the power to conduct searches and seize evidence, even when done during an arrest that turns out to have violated state law.

The unanimous decision came in a case from Portsmouth, Va., where city detectives seized crack cocaine from motorist David Lee Moore after arresting him for a traffic ticket offense.

Justice Antonin Scalia said that when officers have probable cause to believe a person has committed a crime in their presence, the Fourth Amendment permits them to make an arrest and to search the suspect to safeguard evidence and ensure their own safety.

Moore was convicted on a drug charge and sentenced to 3 ½ years in prison. The Virginia Supreme Court had ruled police could not lawfully conduct a search.