ANAHEIM, Calif. (AP) – Detectives have reopened an investigation of the unsolved killing of a Southern California woman 20 years ago.

Eighteen-year-old Mariana Tapia vanished on July 2, 1999, after attending a friend’s birthday party at a nightclub in Pico Rivera.

The mother of a 4-year-old daughter was last seen dancing with unknown men.

A worker inspecting a fence in a brushy area in Anaheim found her body on Aug. 22, 1999. One foot was protruding from a shallow grave. Authorities determined she died from at least one gunshot wound.

Anaheim police say Tuesday that cold case detectives have been re-examining ballistic and DNA evidence, and hope any reluctant witnesses come forward.

Sgt. Jeff Mundy says in particular they hope a woman who called in information in early 2000 calls police again.