BLACKSBURG, Va. (AP) — The gunman who walked up to a police car and shot a Virginia Tech officer to death fled to nearby university greenhouses, where he changed clothes. Despite his attempt to throw off a police manhunt, a patrolling sheriff's deputy spotted him and the gunman killed himself.

State police on Friday laid out their most detailed account so far of the shooting that locked down the campus for several hours. It was the first shooting at the school since it was the scene of the deadliest gun rampage in modern U.S. history that claimed 33 lives in 2007.

Investigators still don't know of any connections between the gunman, whom they haven't named, and university police officer Deriek W. Crouse, 39. The trained firearms and defense instructor with a specialty in crisis intervention had pulled over a driver for a traffic violation when he was killed. There was no link between the driver and the gunman.

Police spokeswoman Corinne Geller said investigators are confident they know the shooter's identity, but they are waiting for final confirmation from a medical examiner before they release it. They know he wasn't a student, but they don't why he targeted Crouse.

"That's very much the fundamental part of the investigation right now," Geller said at a news conference.

It's likely the shooter was the same man who stole a rental car at gunpoint earlier Thursday in Radford, about 15 miles from Blacksburg, Geller said.

Crouse had pulled over a car driven by a student and was stopped on a campus parking lot with that car in front of his cruiser, Geller said. The driver has been very helpful to investigators, she said.

Crouse was sitting in his cruiser when the gunman walked up and shot him. Geller declined to say if the officer was wearing body armor or where exactly he was shot. He was not able to return fire, she said.

Authorities have in-car video from Crouse's cruiser that shows a man with a handgun at the officer's car at the time of the shooting.

The gunman fled on foot and went to nearby greenhouses, where investigators say he changed out of a pullover and wool cap and left them behind with his backpack.

Geller said a deputy sheriff on patrol later noticed a man at the back of another parking lot about a half-mile from the shooting. The man was by himself, looking around furtively and acting "a little suspicious."

The officer drove around to approach him, lost sight of the man and then found him on the ground. The man appeared to have a self-inflicted gunshot wound and a handgun was nearby.

Crouse was an Army veteran and married father of five children and stepchildren. He joined the campus police force in October 2007. He previously worked at a jail and for the Montgomery County sheriff's department.

Crouse was one of about 50 officers on the campus force, which also has 20 full- and part-time security guards. He received an award in 2008 for his commitment to the department's drunken driving efforts. He was trained as a crisis intervention officer and as a general, firearms and defensive tactics instructor.

The university also said its counseling center would be open all day Friday for students.

"A lot of people, especially toward the beginning, were scared," said Jared Brumfield, a 19-year-old freshman from Culpeper, Va., who was locked in the Squires Student Center.

The events 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 stone plaza memorial for the 2007 victims. An official vigil is planned for Friday night.