America's top court does not want cops forcibly extracting blood from motorists without a warrant. The Supreme Court on Wednesday found Tyler McNeely's constitutional rights were violated when he was taken to a hospital for a blood draw after a Missouri state patrolman accused him of driving under the influence of alcohol (DUI) in October 2010.

The state trooper says McNeely was speeding and weaving across the centerline at around 2:08am on that fateful day. McNeely's speech was slurred, he smelled of alcohol and he failed the standard field sobriety tests. The officer wanted a breath test, but McNeely declined. At a hospital, McNeely also refused a blood tests. The blood was taken anyway and his blood alcohol content (BAC) was measured at 0.15. The officer never sought a warrant.

Prosecutors argued no warrant was needed because the situation involved "exigent circumstances" in which the alcohol was evaporating from his blood at a rate, generally, of 0.02 percent per hour. The state wanted an automatic rule allowing police to take blood by force from anyone suspected of DUI, regardless of individual circumstances. The majority saw no reason why a warrant could not have been obtained in this routine DUI case, a decision that resolved differing conclusions arrived at by various state courts.

"Because a police officer must typically transport a drunk-driving suspect to a medical facility and obtain the assistance of someone with appropriate medical training before conducting a blood test, some delay between the time of the arrest or accident and the time of the test is inevitable regardless of whether police officers are required to obtain a warrant," Justice Sonia Sotomayor wrote for the majority. "This reality undermines the force of the state's contention, endorsed by the dissent, that we should recognize a categorical exception to the warrant requirement because BAC evidence is actively being destroyed with every minute that passes. Consider, for example, a situation in which the warrant process will not significantly increase the delay before the blood test is conducted because an officer can take steps to secure a warrant while the suspect is being transported to a medical facility by another officer. In such a circumstance, there would be no plausible justification for an exception to the warrant requirement."

The majority insisted having a neutral magistrate serve as a check on police discretion is essential. It emphasized the availability of technical advances that speed up the warrant application process.

"In short, while the natural dissipation of alcohol in the blood may support a finding of exigency in a specific case, as it did in Schmerber, it does not do so categorically," Sotomayor concluded. "Whether a warrantless blood test of a drunk-driving suspect is reasonable must be determined case by case based on the totality of the circumstances.

A copy of the decision is available in a 250k PDF file at the source link below.