The Los Angeles County Board of Supervisors approved a $20,000 reward this week for information leading to the arrest or conviction of whoever gunned down a young couple in Lancaster last fall.

Supervisor Kathryn Barger recommended the reward, saying investigators have no viable clues but believe witnesses may have seen the suspects or know who they are.

Around 1:45 a.m. last Sept. 30, 18-year-old Andrew Chavez and his girlfriend, 19-year-old Clotee Reyes, had just left an impromptu birthday party in the 43000 block of Sixth Street East and were talking with friends on the street when someone fired shots into the group from a black sedan traveling northbound.

Both Chavez, who lived in Lancaster, and Reyes, who was from Palmdale, were shot in the chest and died at the scene.

Sheriff’s officials said there was some kind of argument outside before the shooting occurred.

In the weeks after the shooting, a sheriff’s lieutenant told the Los Angeles Times that the couple may not have been the shooter’s intended targets.

“There was just indiscriminate gunfire and we think they were caught in the middle of it,’’ Lt. Derrick Alfred of the Sheriff’s Homicide Bureau told the newspaper.

Barger urged anyone with information to call Lt. Derrick Alfred at (323) 890-5500 or Crime Stoppers at (800) 222-TIPS (8477).