Phoenix police trying to catch a serial killer who has shot seven people dead and wounded two others have released 911 calls about two shootings in an effort to generate tips about the suspect.

In one call released Wednesday about a March 18 attack, the victim's sister cries as she tells a dispatcher about the shooting and says she did not see the gunman.

A man living nearby reported being awakened by 11 or 12 gunshots and hearing a vehicle speed away.

Authorities say they have received 3,000 tips about the shootings that happened between March and July.

But police spokesman Sgt. John Howard says detectives have received fewer tips in recent months and hope releasing the 911 audio will generate more.

Detectives are still analyzing tips and evidence.