BLACKSBURG, Va. - Police identified a part-time college student Friday as the Virginia Tech gunman who shot a police officer to death and then killed himself, triggering a lockdown on the campus that witnessed the United States' worst mass slaying in recent memory four years ago

The day before Thursday's shootings, 22-year-old Ross Truett Ashley stole a sport utility vehicle at gunpoint from a real estate office in nearby Radford, where he attended Radford University, police said. The car was found Thursday on the Virginia Tech campus.

Police said Ashley walked up to the police officer 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 shot himself.

Neighbour Nan Forbes said Ashley was quiet, rarely seen or heard from. She said she knew he was in trouble when she saw two police officers guarding the door to his apartment.

"It does freak us out because we live in this building, but there was not one peep of trouble, nothing unusual," she said.

Deriek W. Crouse, 39, was the police officer killed. He had been on the Virginia Tech force for four years, joining about six months after 33 people were killed in a classroom building and dorm April 16, 2007.

Crouse pulled over a student Thursday and was shot while sitting in his unmarked cruiser. The student didn't have any link to the gunman, state police spokeswoman Corrine Geller said Friday at a news conference.

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 they were told to stay indoors.

Fifteen minutes after the witness called police, a deputy sheriff noticed a man at the back of another parking lot nearby. The man was by himself, looking around furtively and acting "a little suspicious," according to Geller.

The deputy drove up and down the rows of the sprawling parking lot and lost sight of the man for a moment. The deputy then found the man lying on the pavement, shot to death. The handgun was nearby.

Police said nobody witnessed the suicide.

The shootings unfolded on the same day Virginia Tech officials were in Washington, fighting a federal government fine over their handling of the 2007 massacre, and the shooting brought back painful memories. About 150 students gathered silently Thursday night for a candlelight vigil on a field facing the memorial for the 2007 victims.

"Why Tech, why again?" said Philip Sturgill, a jewelry store owner. "It's so senseless. This is a lovely, lovely place."

An official vigil was planned Friday night.

School spokesman Larry Hincker said the alert system worked exactly as expected.

"It's fair to say that life is very different at college campuses today. The telecommunications technology and protocols that we have available to us, that we now have in place, didn't exist years ago," he said. "We believe the system worked very well."