The Supreme Court stands before decision was released vacating a death penalty conviction finding that the man’s lawyer violated his constitutional rights by ignoring his objections and telling jurors the defendant killed the victims in Washington, U.S., May 14, 2018. REUTERS/Joshua Roberts

WASHINGTON (Reuters) - The U.S. Supreme Court on Monday limited the ability of police to search rental cars driven by someone other than the person who signed the rental agreement, shoring up privacy rights behind the wheel.

The nine justices unanimously threw out a lower court ruling that had approved of a search by Pennsylvania police of a Ford Fusion driven by Terrence Byrd, whose girlfriend had rented the car. State troopers told Byrd they could search the car because he was not listed as an authorized driver, and they found heroin and a bulletproof vest in the trunk.

Writing for the court, Justice Anthony Kennedy said the “mere fact that a driver in lawful possession or control of a rental car is not listed on the rental agreement will not defeat his or her otherwise reasonable expectation of privacy.”

At issue was whether police violated the U.S. Constitution’s Fourth Amendment, which protects against unreasonable searches and seizures.

The justices sent the case back to the lower courts to determine whether police had the proper justification to search the car without a warrant because they believed there was evidence of a crime. Byrd pleaded guilty in 2014 to unlawful possession of both items on condition that he could challenge the search.

Byrd’s girlfriend rented the car in Wayne, New Jersey in September 2014, handing the keys to Byrd, who was stopped on his way to Pittsburgh.

A federal trial judge denied Byrd’s bid to suppress the evidence because the search violated his constitutional rights. The Philadelphia-based 3rd U.S. Circuit Court of Appeals upheld that ruling last year, prompting Byrd’s appeal to the Supreme Court.