PORTLAND — Maine’s supreme court has overturned the drunken driving conviction of a motorcyclist who was stopped by a trooper seeking information about a speeding motorist.

The Supreme Judicial Court ruled unanimously today that prosecutors couldn’t use evidence obtained when the trooper stopped Robert LaPlante on Route 179 in Hancock County to ask which way the speeding motorist had turned. The trooper realized LePlante had been drinking, gave up the pursuit and turned his attention to him.

LaPlante contended the traffic stop violated his rights as an unreasonable seizure of his person, but a judge denied LaPlante’s motion to suppress the evidence in 2003.

The supreme court saw the case differently, ruling that a trooper’s investigation of another motorist’s speeding offense did not, standing alone, justify LePlante’s traffic stop.