Sierra, who attended Schurr High School in Montebello, was on her way to school when she was snatched off the street and murdered in October 2002.
"This essentially is in retaliation for the community's cooperation with law enforcement," said Lt. Dave Coleman with the Los Angeles County Sheriff's Department at a Friday news conference. Sheriff's officials released new composite sketches of two men who might know something about the murder.
Deputies also said they're trying to track down another person, George Barraza, who is wanted for questioning about the murder. Authorities are also looking for two women who may have been involved in the initial kidnapping.
"Because new witnesses have come forward, investigators were able to develop this. In the past, we've sought help from the community and help has come forward," said Coleman. Detectives also said they have DNA evidence they hope will provide more leads in the case.
Sierra's mother and sister attended the news conference and pleaded for the public's help in solving the case.
"I promised my sister when I was burying her that I will not stop until I've brought justice to her, and I will continue to strive to bring justice to her," said Sierra's sister, Fabiola Saavedra.
Investigators said an East L.A. street gang was trying to warn the community about cooperating with law enforcement. So they used Sierra to send a message.
"She was an innocent victim. She had nothing to do with it," said Coleman.
The teenager's body was found one day after her kidnapping in Crestline in San Bernadino County. Ten years have passed since the murder, but investigators are hoping people will come forward with information.
If you have any information regarding this case, you're urged to contact the Los Angeles County Sheriff's Department's Homicide Bureau at (323) 890-5500.