A man shot dead a woman passenger, then fatally shot himself in the head while speeding along an Orange County freeway and his car careened off the roadway without hitting other vehicles, authorities said. Anaheim police detectives had discovered no motive for the murder-suicide on the Riverside Freeway and had not determined the relationship between the dead man and woman, Sgt. Gordon Blair said. Police went to investigate a report of a car that had driven off the eastbound freeway lanes near Lakeview Avenue, Blair said. Officers found the car had gone up an embankment and stopped when it lost its momentum, he said. "Based on evidence, detectives believe the driver shot and killed the passenger, then turned the gun on himself . . ." Blair said. The dead driver was identified as Gustavo Suarez, 21, of Huntington Beach. The woman was Rosalba Martinez, 25, of Anaheim.