WASHINGTON – A closely divided Supreme Court ruled Thursday that police do not need a warrant before using blood drawn from an unconscious driver to prove he was intoxicated.

The court, in a 5-4 decision, ruled that blood can be drawn from an unconscious driver who cannot be given a breath test because such a situation is urgent enough to eliminate the need for a warrant. Associate Justices Sonia Sotomayor, Ruth Bader Ginsburg, Elena Kagan and Neil Gorsuch dissented in the decision, authored by Associate Justice Samuel Alito.

Blood tests are the only way to reliably test the alcohol level consumed by unconscious drivers — "surely the most dangerous class of drivers," Alito said from the bench in announcing the ruling on the last day of the term. Waiting for a judge to sign off on a warrant, or for a driver to become conscious, would result in "less reliable" blood test results.

"Police officers most frequently come upon unconscious drivers when they report to the scene of an accident, and under those circumstances, the officers' many responsibilities – such as attending to other injured drivers or passengers and preventing further accidents – may be incompatible with procedures that would be required to obtain a warrant," Alito said. "Thus, when a driver is unconscious, the general rule is that a warrant is not needed."

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The case involved Wisconsin's Gerald Mitchell, who was under the influence of both drugs and alcohol and was found drunkenly wandering along the shore of Lake Michigan in May 2013. Police took him to a hospital for a blood draw, but by then he was unconscious.

Drivers in Wisconsin are presumed to have consented to a blood draw simply by taking the wheel. They can withdraw that consent at the risk of losing their license, but that doesn't apply to unconscious drivers. Twenty-eight states have similar "implied consent" laws.

Mitchell was convicted of driving while intoxicated, and state courts upheld the conviction. But the Supreme Court agreed to decide whether implied consent is consistent with the Fourth Amendment's ban against unreasonable searches.

On one side were law-and-order types such as Chief Justice John Roberts and Alito, who saw little wrong with the state's approach. Associate Justice Clarence Thomas sided with the court's conservative wing, writing in a concurring opinion that the Supreme Court has consistently ruled that police officers may perform searches without warrants "when destruction of evidence is at risk."

"The rule should be no different in drunk-driving cases," Thomas wrote.

On the other side were most of the court's liberal justices and Gorsuch, who has taken up the late Justice Antonin Scalia's penchant for protecting criminal defendants' rights.

In her dissenting opinion, Sotomayor said the court faced a narrow question.

"What must police do before ordering a blood draw of a person suspected of drunk driving who has become unconscious?" Under the Fourth Amendment, the answer is clear: If there is time, get a warrant," Sotomayor wrote.

Mitchell's appeal attracted support from defense lawyers and libertarian groups, while Wisconsin drew the backing of 18 states, Wisconsin municipalities and Mothers Against Drunk Driving.