An 80-year-old man who stayed free for more than 40 years after the sexual assault and murder of a 15-year-old girl is headed to prison for life after DNA on discarded gum finally tied him to the crime.
Mark Stanley Personette was sentenced Wednesday to life in prison for the 1978 sexual assault and killing of Marissa Harvey in San Francisco, ending a cold case that spanned nearly half a century.
Harvey, a 15-year-old from New York, was visiting her older sister when she went for a day trip to Golden Gate Park for horseback riding and never came back. The next day, surfers found her body in nearby Sutro Heights Park. Prosecutors said she had been sexually assaulted, beaten, and strangled with a ligature.
Personette, arrested in Denver in December 2021, spent decades outside custody before advanced DNA work and investigative genealogy put a name to the evidence left on the teenager’s clothing and on dried gum stuck to her back.
San Francisco police used the best tools they had at the time and ran down every lead. The case still went cold.
In the early 2000s, DNA testing produced a male profile from Harvey’s sweater and jeans and from that dried gum. Investigators had a genetic signature. They did not have a suspect.
Nearly 20 years later, police turned to investigative genealogy and public genetic databases, the same approach that helped catch the Golden State Killer in 2018. That work pointed to Personette.
Prosecutors said the case reopened in 2021 once he was identified as a suspect through the advanced DNA testing and genealogy work.
FBI investigators then watched Personette throw away trash at a Walmart parking lot more than 15 miles from his home. They recovered discarded personal hygiene items. DNA from those items matched the profile from Harvey’s clothing and the gum.
A warrant followed. In December 2021, 43 years after the killing, officers arrested him in Denver, Colorado.
Daily Mail reporting detailed what else turned up around him: a 1970s map of San Francisco inside his home, along with California license plates carrying a 1979 registration sticker. Personette denied ever visiting the city.
At trial, another woman testified that Personette raped her in a wooded area of New Jersey when she was 16 years old in 1979. A 1979 booking photo was also referenced in the case material.
After the arrest, police said they believed he may have had more victims. They urged law enforcement agencies nationwide to review unsolved sexual assault-related homicides involving young women.
San Francisco District Attorney Brooke Jenkins hailed the life sentence in a statement released by her office.
Jenkins said:
"After almost 50 years, Mr. Personette is finally being held accountable for his heinous crimes against Marissa and will spend the rest of his life in prison,"
She added:
"While nothing can bring Marissa back to her family, today’s sentence hopefully leaves her family with a sense that justice was done for all that they have endured."
Harvey was a teenager on a family visit who never made it home from a park outing. Personette lived free into old age until the gum, the clothing evidence, the genealogy work, and the trash DNA closed the circle.
When predators think time will bury the truth, patient police work and hard evidence can still deliver the only verdict that fits.
