San Francisco  - Police were on Monday investigating why a man opened fire on a line of teenagers waiting to enter a nightclub, killing two teenage girls and wounding seven others before shooting himself in the head.

The incident took place Saturday night in Portland, Oregon. The perpetrator was named as Erik Salvador Ayala, 24, of Milwaukee, Wisconsin.

Police have not established any relationship between him and the victims. According to The Oregonian, Ayala had no criminal record and had not been in the nightclub before the Saturday night shooting.

His roommates said he was a quiet man, who enjoyed video games but had never shown any violent tendencies and did not own a gun.

One of the dead girls was a local high school student. The other was a 17-year old exchange student from Peru. A third exchange student from Italy was critically wounded in the attack.

They were waiting to get into The Zone disco to celebrate the birthday of a Guatemalan exchange student that night.

Police chief Rosie Sizer called the shooting "a random act of violence of the kind that makes you despair for America." (dpa)