In 1989, Ramirez was convicted of 13 murders, two in San Francisco and 11 in Southern California. The new accusation involves the death of 9-year-old Mei Leung in 1984. Leung was sexually assaulted and killed in the basement of her family's Tenderloin neighborhood home.
The case remained unsolved for 25 years until new information began pointing toward Ramirez. San Francisco police investigators reopened the case and ran old DNA evidence from the crime scene through the DNA databease and it matched Ramirez.
Wednesday, Investigators served a warrant for a new DNA sample from Ramirez. The results will not be in for a few weeks.
"A new sample from Mr. Ramirez was collected, what we will now do in the laboratory is analyze that sample here at the local lab and compare it directly to the crime scene evidence," San Francisco police lab technician Matthew Gabriel said.
Investigators say they spent five years working on this part of the investigation before making Thursday's anouncement.
Ramirez is currently in San Quentin State Prison, awaiting execution.