Police used spit from the sidewalk to link a suspect to the murders of two women six years ago.
17-year-old Michelle Lozano was murdered in 2011.
The body of 22-year-old Bree'Anna Guzman was found five months later.
DNA was found at both crime scenes but the cases remained unsolved.
Detectives recently used a process known as familial DNA testing which can identify likely relatives of a suspect.