Personal Hygiene Products Thrown Out in a Walmart Parking Lot Helped ID a 15-Year-Old's Killer Almost 50 Years Later

It would take nearly five decades for detectives to catch New York teen Marissa Harvey’s elusive murderer.

The 15-year-old from Long Island, N.Y., was visiting her sister in San Francisco when she was raped and killed. Harvey had planned to go horseback riding on the afternoon of March 27, 1978, according to the San Francisco District Attorney’s Office. She was last seen alive that day by her sister’s friend, who dropped her off at the Golden Gate Park, SFGATE reported. She never made it back home.

A group of surfers found Harvey’s body the next day, about a half mile away in Sutro Heights Park. The coroner determined she had been “badly beaten” and strangled to death with a cord, the San Francisco Chronicle reported. She was also brutally sexually assaulted.

“There was a significant amount of sperm DNA found on her clothing,” Lt. Alan Levy with the San Francisco Police Department (SFPD) tells A&E Crime + Investigation. A piece of dried gum belonging to the killer was also located on Harvey’s back.

Detectives utilized the most advanced technology available at the time, exhausted every possible lead and investigated several persons of interest, but the case subsequently went cold.

It wasn’t until 2020, when breakthroughs in DNA technology and investigative genealogy allowed for the SFPD to reopen Harvey’s case with Levy at the helm.

“We started utilizing this technology, and due to the amount of DNA we had, we thought that this would be a viable option to pursue,” Levy says. “With these advanced forensic methods, we were able to determine a likely perpetrator.”

Evidence indicated that likely perpetrator was Mark Personette, now 80.

“He wasn't even on our radar because he was somewhat transient between the East and West Coast,” Levy says.

Finally, in December 2021, investigators tracked Personette down in Denver.

“What made it difficult was that he was in the mountains of Colorado,” he says. “To find him and obtain a DNA sample from him, we had to be patient, we had to be methodical and we had to make sure that it was done correctly.”

Authorities were led to a location 15 miles away from the suspect’s residence.

“We surveilled him for a period of time and followed him to a Walmart parking lot where he discarded his trash, and it was within this trash that we were able to obtain a DNA sample from him that matched the perpetrator we had from all the sperm DNA on the victim,” Levy says.

A search of Personette’s home revealed he was intentionally separating his personal hygiene items—dental floss, tissues and cottons swabs— from the rest of his trash because he “may have been paranoid” that he’d someday be linked to the crime, Levy surmises.

At the scene, authorities also recovered what appeared to be souvenirs from Personette’s attack on Harvey: a map of San Francisco from the 1970s, as well as California license plates with a 1979 registration sticker, according to the San Francisco District Attorney’s Office.

“For more than four decades, Marissa Harvey’s family members have been relentless advocates to bring her killer to justice, and we hope this development in the case begins to bring a measure of healing and closure they’ve been too long denied,” San Francisco Chief of Police Bill Scott said in press release announcing Personette’s arrest in 2021.

Levy says Harvey’s family was “extremely happy, grateful and relieved” they finally caught her killer.

With further investigation, it became apparent that Harvey wasn’t Personette’s only victim. Citing criminal history records, authorities were able to connect him to another sexual assault of a 16-year-old girl in New Jersey in 1979, who happened to survive the harrowing attack.

She took the stand at Personette’s trial in November 2025.

“The fact that she came to San Francisco and testified in a court room shows how extremely brave she is,” Levy says.

Authorities believe Personette targeted victims of opportunity and that there still may be others.

“It was a matter of chance. He likely came across them and they were alone,” he says.

San Francisco Assistant District Attorney Katherine Wells slammed Personette’s decades-long attempt to elude authorities and the bizarre effort to separate his trash.

“If you happen to be somebody who ejaculated into and killed a 15-year-old-girl in 1978, totally unaware of the idea of DNA, and then in 2018, 2019, 2020 you start seeing big national news that the Golden State Killer was caught because he left a tissue in his garbage can and the FBI picked it up, you might start worrying about that. You might start changing your behavior,” Wells told the court during Personette’s trial, San Francisco Public Safety News reported. “This is all consciousness of guilt.”

In November 2025, Personette was convicted of Harvey’s murder.

“You have to acknowledge the true grit and determination of homicide investigators that tirelessly worked this case,” Levy points out. “It was probably one of the most challenging cases I endeavored because we were trying to reverse engineer and reconstruct an incident from 1978. The investigators who worked prior to me did such a great job, it came together in an orderly fashion.”

Following the conviction, Personette fired his defense attorney and acquired new legal representation, triggering a delay in sentencing. Jail records indicate that he continues to be held at the San Francisco County Jail.