BLACKSBURG, Va. – Police identified the Virginia Tech gunman Friday as a part-time college student from nearby Radford University, although they still have not been able to say what led him to kill a police officer and then himself.

The day before Thursday’s shooting and campus-wide lockdown, Ross Truett Ashley, 22, stole a sport utility vehicle at gunpoint from a real estate office in Radford, police said. He dumped the car on the Virginia Tech campus and it was found Thursday.

Police said that same day he walked up to the patrolman he did not know and fired, then took off for the campus greenhouses, ditching his pullover, wool cap and backpack. He made his way to a nearby parking lot and when a deputy spotted him, he took his own life, leaving fresh questions on a campus still coping with the nation’s worst mass slaying in recent memory.

Why didn’t he run or engage the deputy who closed in? Was he even aware that thousands of students had just been alerted by cellphone that a gunman was on the loose and the campus was locked down? And why did he shoot an officer at a school he never attended?

“That’s very much the fundamental part of the investigation right now,” state police spokeswoman Corrine Geller said Friday at a news conference.

Deriek W. Crouse, 39, was the slain officer. Crouse was a trained firearms and defense instructor with a specialty in crisis intervention. He had been on the force for four years, joining about six months after 33 people were killed in a classroom building and dorm on April 16, 2007.

At 12:15 p.m. Thursday, Crouse pulled over a student and was shot while sitting in his unmarked cruiser. The student didn’t have any link to the gunman, Geller said.

Shortly before 12:30 p.m., police received a call from a witness who said an officer had been shot. About six minutes later, the first campus-wide alert was sent by email, text message and electronic signs in university buildings. Many students on campus were preparing for exams, and some described a frantic scene after the initial alert. Soon, heavily armed officers were walking around campus and caravans of SWAT vehicles were driving around.

Students outdoors went inside buildings. Those already there stayed put. Everybody waited.

Police said nobody witnessed the suicide, the parking lot apparently vacant because of warnings. For three more hours, students checked their phones, computers and TVs. Finally, the school gave the all clear.