We wrote in February about the issue pending before the United States Supreme Court in Missouri v. McNeely: whether police can dispense with a search warrant and draw blood from an individual suspected of driving while intoxicated.

Well, in April, the Supreme Court ruled and in a decision authored by Justice Sotomayor held that usually police must obtain warrants in such situations.

The underlying Missouri prosecution concerned a gentleman named Tyler McNeely. He was driving his car--speeding and swerving at the same time, it seems --when he was pulled over by a state trooper in Cape Girardeau County. Mr. McNeely had two previous DWI convictions, but this time he refused to submit to a breathalyzer test so that his blood alcohol level could be ascertained.

The arresting officer administered some field sobriety tests, which McNeely apparently failed. McNeely was also described as being unsteady on his feet and having slurred speech.

There is little doubt that under these facts that a warrant for a blood test could have been obtained readily and quickly. During the Missouri suppression hearing below, McNeely’s counsel entered into evidence a search warrant form used by the police in DWI cases and the arresting officer acknowledged that he had used these forms in the past and that they were “readily available.”

But the police chose not to seek a warrant. Instead, they handcuffed McNeely and drove him to a local hospital where blood was drawn. Mr. McNeely refused to consent to the blood test, but the police directed the lab technician to take the sample nonetheless. The test results indicated a blood alcohol level about twice Missouri’s legal limit.

At trial, the Missouri lower court threw out the blood test results, holding they were the product of an unreasonable search and seizure, a finding later upheld by the Missouri Supreme Court.

The State of Missouri sought review in the Supreme Court asking the Court to endorse a per se rule that would allow for blood testing without a warrant—the rationale for this being the natural physiological processes by which alcohol dissipates in human blood, thus destroying potential evidence.

This rationale, however accurate it might be as a matter of basic biology, failed to carry the day, as Justice Sotomayor wrote that the natural dissipation of alcohol in the human bloodstream is not enough of an exigency to dispense across-the-board with the requirement that police get a judge’s permission before drawing blood. This finding is consistent with a significant number of state statutes that prohibit warrantless blood tests, in all or the majority of circumstances. Only Justice Thomas dissented from the Court’s ruling.

So, are warrantless blood tests now off-limits in all instances? Maybe and maybe not. The proverbial door was left slightly ajar as to whether there could be exigent circumstances where a lack of a warrant would not be fatal to a blood test’s admissibility, although the Court did not elaborate on what exactly these might be. Justice Kennedy did mention in a separate opinion that some further definition may need to come in the future.