Suspected killer identified in 1992 cold case slaying of an Alameda woman

Side by side photos of woman and a man.
Juliette Rivera and Gregory Marc Riviera. Rivera’s body was found in July 1992 and Riviera was a person of interest in the investigation.
(San Mateo County Sheriff’s Department)

A suspect has been identified in the 1992 cold case slaying of an Alameda, Calif., woman, according to the San Mateo County Sheriff’s Office.

Gregory Marc Riviera, 50, who died earlier this year, was identified using fingerprints as the suspect in the killing of 25-year-old Juliette Rivera, the sheriff’s department said in a news release.

Riviera evaded arrest for 30 years in connection with the killing by assuming his brother’s identity, authorities said.

The case began when the sheriff’s department launched a missing person investigation for Rivera on July 7, 1992, authorities said. Investigators contacted Riviera, an acquaintance of Rivera’s.

Police said they began to suspect Riviera was involved in the woman’s disappearance due to inconsistencies in his statements to detectives.


A woman’s body was found July 17, 1992, by a farmworker in a rural area of unincorporated San Mateo County, according to authorities. The body, which was badly decomposed, was later identified as Rivera. An autopsy showed that she suffered from blunt force trauma to her left rear skull from a flat object.

A warrant was issued for Riviera, charging him with the slaying, but he had abandoned his apartment on July 29, 1992, and went missing for 30 years, police said.

On May 12, 2022, the San Mateo County Sheriff’s Office got a call from the Merced County Coroner’s Office, saying that an unsheltered man identified as Jon Paul had passed away earlier this year, according to officials. The coroner found that the man’s fingerprints matched Gregory Riviera’s.

The coroner’s office found a warrant for Riviera’s arrest and worked with sheriff’s detectives to confirm his identity, according to police. During the investigation, detectives discovered that Riviera had a brother named Jon Paul, who was still alive but dealing with medical issues, Jon Paul’s daughter told the coroner.

Jon Paul Riviera’s daughter also told police that Gregory Marc Riviera and her father used each other’s identity for 30 years to evade authorities.

“The closure of this 30-year-old cold case homicide could not have been possible without the assistance of the Alameda Police Department, the Merced County Sheriff’s Office and Coroner Bureau, and the San Mateo County district attorney’s office,” the San Mateo County Sheriff’s Office said in a statement. “Thank you all for your collaboration and tremendous work.”