Authorities are still sorting out why a Virginia Tech police officer was killed in a campus parking lot by a gunman who then apparently shot himself to death. The university last night identified the officer as Deriek W. Crouse, a 39-year-old Army veteran and married father of five who joined the campus police force about six months after the 2007 shooting rampage that left 33 people dead. Crouse was killed after pulling a driver over in a traffic stop. The gunman, who wasn’t involved in the traffic stop, walked into the parking lot and ambushed the officer. Before it became clear that the gunman in yesterday’s attack was dead, the school locked down the campus and used a high-tech alert system to warn students and faculty members to stay indoors.