The Monterey County Sheriff's Department says 19-year-old Juan Salazar Jr. and Eunice Serrato surrendered Saturday morning at the San Ysidro border crossing.
Investigators initially believed the girl was abducted by her boyfriend after two men were killed at the San Ardo home where she was staying. Their bodies were discovered on July 28.
Details of the killings and their motive haven't been released.
On Friday, a Paso Robles woman was arrested in connection with the case. Thirty-six-year-old Maria Aviles-Rodriguez was arrested on suspicion of aiding a kidnapping, child abuse and other crimes.