As if it were an open question, the Supreme Court today reaffirmed the principle that warrants are required before the police conduct a search or seizure under the Fourth Amendment, except in certain limited circumstances.
Criminal defense lawyers have long complained that the exceptions swallow the rule, such that warrants are rarely required in fact, even though on a law school exam you’ll be given all sorts of nifty scenarios wherein you’re asked to test the constitutionality of a hypothetical search.
When are warrants not required? Consent: If you tell a police officer, “It’s ok to search my home,” then you’ve effectively given up your Fourth Amendment rights in that situation so long as the consent was given voluntarily. If observable or detectable evidence is likely to be destroyed if police take the time to get a warrant, then a search warrant may not be necessary.
In Schmerber v. California, the Supreme Court held that where there are exigent circumstances, police may be able to draw blood absent a warrant especially where the dissipation of evidence may occur before a warrant can be secured. But the Court held that exigent circumstances must be established by a totality of circumstances analysis – how difficult it might be to get a warrant, the backup at the jail that might prevent blood being drawn, the proximity of the scene of the DWI stop to the jail versus to a hospital, and so forth.
Missouri sought to bypass that entire analysis by creating a per se rule that any time a DWI is suspected, police may pull blood without a warrant.
In drunk-driving investigations, the natural dissipation of alcohol in the bloodstream does not constitute an exigency in every case sufficient to justify conducting a blood test without a warrant.