(Reuters) - DNA evidence has cleared a former policeman accused of being the “Golden State Killer,” who terrified a swath of California with dozens of rapes and murders in the 1970s and 1980s, in one murder case from 1975 in which he was a suspect, prosecutors said.

Slideshow ( 2 images )

More than three decades after the spate of killings and home invasions ended, investigators last year tracked down and arrested former police officer Joseph DeAngelo, 73, after comparing DNA found at crime scenes to data on commercial genealogy websites. So far they have charged him with 13 counts of murder and kidnapping from 1975 through 1986.

Investigators have ruled out DeAngelo as a suspect in the 1975 murder of 14-year-old Donna Jo Richmond based on DNA evidence, according to a press statement from the Tulare County District Attorney’s office. Investigators are still seeking to determine whether he can be linked to other crimes from that time.

Prosecutors are standing by the conviction of Oscar Clifton for murdering Richmond while she was riding her bike near Exeter, California, on Dec. 26, 1975.

Clifton, who always maintained his innocence, was sentenced to life in prison and died in 2013.

“We feel that Mr. Clifton received a fair trial and that the evidence more than sufficiently points to his guilt,” Ward said in a televised statement on Tuesday.

DeAngelo has not yet entered a plea related to the charges he faces.

The District Attorney’s conviction review report, reviewed by Reuters, said a DNA profile developed in 2011 from a sample found on Richmond’s body does not match DeAngelo’s genetic profile, clearing him of suspicion.

Neither Ward nor Tony Reid, a former lawyer for Clifton, immediately responded to a request for comment on Wednesday.

DeAngelo was arrested in April and charged with 13 counts of murder and 13 counts of kidnapping, with “special circumstance” allegations making him eligible for capital punishment.

Detectives followed the family trees of close matches on the genealogy websites, seeking people who might be the killer. The process produced a promising lead in April, when the DNA of a relative pointed to DeAngelo based on his age and the fact that he lived near where the attacks occurred, the chief deputy district attorney for Sacramento County said.