MORRISON, Colo. (AP) — Authorities were searching Friday for a gunman who shot and wounded three people at the end of a rap concert at the popular Red Rocks outdoor amphitheater near Denver.

No motive was released, but Jefferson County sheriff’s spokesman Mark Techmeyer said the attack did not appear to be random.

The victims’ injuries were not life-threatening. Their names were not released.

The shooting occurred Thursday night at the concert benefiting three groups, including the Gang Rescue and Support Project of Denver.

“We want to know what’s going on so we can help out in any way,” said Cisco Gallardo, director of the gang rescue group. “There could have been (a) prior beef, prior problems.”

The injured people were in a white sport-utility vehicle and drove themselves from Red Rocks to a Denver intersection about 15 miles away, but it was not clear why, Techmeyer said. They were eventually stopped by Denver police and taken to a hospital.

Investigators did not know if more people had been in the SUV before police stopped it.

About 4,500 people attended the concert featuring Nas, Schoolboy Q and Flying Lotus, Red Rocks officials said. The amphitheater seats up to 9,525 people.

Promoters said the gang rescue group got 5 percent of the profits. Two other groups also got 5 percent each: Preserve the Rocks, which helps preserve the Red Rocks venue, and Helping Our People Excel, a Denver-area charity with a food pantry and other services.

Investigators stopped and questioned each car as it was leaving the venue. Traffic was chaotic and slow, but “we had a shooter out there,” Techmeyer said.

Witnesses were interviewed until early Friday.

The amphitheater and surrounding park in the foothills west of Denver are popular with joggers and sightseers. Most of the park had been reopened, but the area of the shooting remained sealed off.

The Beatles and Grateful Dead have performed at Red Rocks, where U2 filmed “Under a Blood Red Sky.”