(CBS) LOS ANGELES A billboard with photos of four young murder victims was unveiled in South Los Angeles Wednesday to raise awareness of gun violence and encourage witnesses to come forward about unsolved murders.

"We as a community are responsible for each and every one of those kids on that billboard, each and every one of these kids you see right here and each and every one of these kids you these parents holding," said Lawanda Hawkins, founder of Justice for Murdered Children, which was created to help mothers of murder victims. "We are responsible for them. We are responsible them being murdered and we're responsible for those who killed them. It's our responsibility to bring those who killed them to justice."

The billboard, which is sponsored by Northrop Grumman, includes a photo of 20-year-old Lori Gonzalez, the granddaughter of former police chief and current City Councilman Bernard Parks.

Other victims on the billboard are Mario Vidal Jr., who was killed in 2004, Teresa Del Rio, 20, who was shot to death in 1999 and 18-year-old Reginald Reese, 18, who was murdered in 1995.

The billboard is located at Crenshaw Boulevard and 52nd Street.