The U.S. Supreme Court rule this month in Missouri v. McNeely, No. 11-1425 that the decision of whether to get a warrant to draw blood in a DUI case will be judged on its own facts. There will be no bright-line rule on whether a warrant is or isn't needed.
According to Lyle Denniston at the SCOTUSBlog, none of the Court’s four opinions — a majority, two separate opinions supporting the result, and one dissenting opinion — said that officers investigating drunk-driving cases must always get a warrant. But the majority did say that the Fourth Amendment does not allow police to get a blood sample without ever having to get a warrant, in any case (as the dissenting opinion suggested). So that sets up the case-by-case approach, suggesting that getting a warrant very likely would remove the doubt.
Justice Anthony M. Kennedy vote was necessary to make a majority for the requirement that each case be judged on its own facts, his separate opinion may have special importance for local governments and their police forces as they decided how to react to the new ruling.
According to Denniston, Kennedy suggested that local officials still retain the authority to work out “rules and guidelines that give important, practical instruction to arresting officers,” and that those kinds of rules might well allow blood testing without a warrant “in order to preserve the critical evidence” of blood alcohol content. As further cases develop, Kennedy wrote, the Court itself might find it worthwhile “to provide more guidance than it undertakes to give today.”
Kennedy's vote supported this conclusion: “always dispensing with a warrant for a blood test when a driver is arrested for being under the influence of alcohol is inconsistent with the Fourth Amendment.”
To read more: http://www.scotusblog.com/?p=162525