An 80-year-old man has been convicted of murder for the death of a 15-year-old girl in San Francisco nearly five decades ago, prosecutors said.

In a statement, the San Francisco District Attorney’s Office announced that a jury found Mark Personette guilty of first-degree murder in the 1978 killing of Marissa Harvey, a teenager visiting her sister in San Francisco when she disappeared after going to Golden Gate Park to ride a horse.

Her body was discovered the next day in the underbrush at Sutro Heights Park.

“At long last, justice has been delivered, and Mr. Personette is being held accountable for this horrific crime,” District Attorney Brooke Jenkins said in a statement Thursday. “Although nothing we do can bring the victim back, I pray this verdict gives the family a sense of closure and inspires others who are still waiting for justice not to lose hope.”

According to evidence presented at trial, Harvey was attacked, sexually assaulted and strangled with a ligature. Investigators recovered her earring, a blood-stained leaf, and other evidence at the site.

“Although nothing we do can bring the victim back, I pray this verdict gives the family a sense of closure and inspires others who are still waiting for justice not to lose hope.” District Attorney Brooke Jenkins

DNA testing decades later revealed a male profile on Harvey’s clothes and on a piece of dried gum stuck to her back. In 2021, investigators identified Personette as a suspect using investigative genealogy.

FBI agents in Denver collected DNA from personal hygiene items he discarded in a Walmart parking lot that matched the crime scene profile. A subsequent search found he kept 1970s maps of San Francisco and old California license plates despite later denying he had been in the state.

A woman had testified that Personette raped her in a wooded area of New Jersey in 1979, about a year after Harvey was killed.

Assistant District Attorneys Heather Trevisan and Katherine Wells prosecuted the case with help from San Francisco police cold case investigators, the FBI, paralegals, victim advocates, and a police support dog named Auburn.

“This case shows that time cannot thwart justice,” Trevisan said, with Wells adding that the verdict proves “time and distance will not shield those who commit heinous acts.”

Personette, who remains in custody, faces seven years to life in prison. His sentencing is scheduled for Dec. 17.