Virginia Tech gunman acted alone, police say
The man who shot dead a police officer before turning the gun on himself at Virginia Tech's campus acted alone, investigators have said.
Police spokeswoman Corinne Geller says they are still trying to determine why Officer Deriek Crouse was attacked.
She told journalists the gunman ran from the scene on Thursday and changed clothes before taking his own life.
The university was the site of the worst US school shooting, in 2007, when a gunman killed 32 people and himself.
Ms Geller told Friday's news conference that the gunman was not a student at Virginia Tech.
But she declined to say more until the medical examiner confirms his identity and next of kin are notified.
Suspect on tape
Investigators have found no link between the gunman and Officer Crouse, a married father of five and 39-year-old Army veteran. The policeman was attacked while performing a routine traffic stop in a car park shortly after midday on Thursday.
The student driving the car had pulled up beside Officer Crouse, who was inside the police car.
The gunman, who was not linked to the car that was pulled over, walked up and opened fire at close range, before fleeing on foot.
It is not known where the officer was wounded or if he was wearing body armour. He did not return fire. However, a video camera inside the officer's vehicle captured footage of the suspect.
Ms Geller said the shooter then changed his clothes in an effort to escape the police, taking off a jumper and woollen cap. He put them in a backpack and left it behind a greenhouse.
He was later spotted by another policeman in a nearby car park. He was alone and looked "suspicious", reports say.
As the policeman approached, the man disappeared from sight and was found on the ground, apparently having shot himself. The gun was found close to the body.
Ms Geller said it is likely the assailant had stolen a rental car at gunpoint about 15 miles from Blacksburg, earlier on Thursday.
On Friday, Virginia State Police said in a news release that "ballistics evidence testing has officially linked the two fatal shootings".
An official vigil is planned on Friday night.
About 150 students gathered in a candlelight vigil on Thursday evening at the campus memorial for the shootings of four years ago.
"Our hearts are broken again," said university President Charles W Steger.
Officer Crouse received an award in 2008 for his commitment to the department's efforts to deter drink-driving. He was trained as a crisis intervention officer and a defensive tactics instructor.
He was one of about 50 officers on the campus force and had served there for four years, joining about six months after the 2007 massacre.
That tragedy prompted the university, which has about 30,000 students, to implement a highly sophisticated security alert system.
After Thursday's initial report of gunfire, the procedure was activated. Texts and emails were sent to staff and students warning them to stay indoors.
The campus was placed on lockdown for several hours as police Swat teams scoured the area.
The bloodshed came on the same day as Virginia Tech appealed against a $55,000 (£35,200) fine imposed by the government for not reacting quickly enough to the 2007 massacre.
Thirty-two people died in April that year when a 23-year-old South Korean, Seung-Hui Cho, went on a gun rampage before turning the weapon on himself.