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ANTIOCH -- Police are seeking the public's help in finding who shot and killed two people in a small stretch of unincorporated Contra Costa County on Sunday evening.

The shooting was reported around 5:25 p.m. on Buchanan Road, just west of the Antioch city limit. Two people were found on the roadway.

The two victims were identified Monday as San Francisco residents Christopher Zinn, 24, and Brieanna Dow, 21. Zinn was pronounced dead about 20 minutes after deputies arrived on the scene; Dow was taken to Sutter Delta Medical Center, where she died about 90 minutes later.

Contra Costa County Sheriff's detectives and crime lab technicians responded to the location, but no suspects or motive have been identified, according to spokesman Jimmy Lee.

Anyone with information about the case is asked to call 925-313-2651. Anonymous callers can leave tips at 866-846-3592.

Contact Daniel M. Jimenez at 510-262-2728. Follow him at Twitter.com/DMJreports.