I do not often find myself in agreement with many of the opinions written by Justice Scalia, but his recent dissent in Navarette v. California is right on target. Navarette started as a DUI investigation, but led to drug charges for the defendants.
The majority opinion, written by Justice Clarence Thomas, allows a search following a forcible stop which was justified solely by an anonymous 911 caller who told the dispatcher that Navarette's truck had "run her off the road." The majority says that the tip, even though uncorroborated by the police, was sufficient to make the stop because the police were justified in believing that Navarette was driving under the influence (DUI). The stop and search led to an arrest for drug charges.
Justice Scalia's dissent shreds this analysis. He points out that the anonymity of the tipster makes the tip less reliable, and the fact that 911 calls can be traced back to an anonymous caller does not make the tip more reliable unless the caller knew the call could be traced back to her if it turned out to be false. Also, unlike other cases where the court had approved a stop based on a tip, there were no real details given by the caller which would suggest reliability.
Scalia also ridiculed the idea that a single instance of careless driving would support the inference that an ongoing DUI episode was occurring. He points out that the police attempted to corroborate the tip by following the truck for five minutes. During that time, they observed spotless driving and no traffic infractions. Their own observations, in other words, undercut the validity of the anonymous tip.
Drunken driving is a serious matter, but so is the loss of our freedom to come and go as we please without police interference. ... After today's opinion all of us on the road, and not just drug dealers, are at risk of having our freedom of movement curtailed on suspicion of drunkenness, based upon a phone tip, true or false, of a single instance of careless driving.
The decision can be read in full here: