Sonoma County 1983 cold case sexual assault, murder solved, deputies say
More than four decades after a Sonoma County man was sexually assaulted and murdered, deputies said they have solved the case.
The Sonoma County Sheriff's Office announced Wednesday that the investigation into the death of 31-year-old Robert Pangborn is officially closed. On May 21, 1983, Pangborn was found fatally stabbed and partially clothed on Riverlands Drive in Guerneville.
Despite what deputies called an "exhaustive" investigation, no suspect was identified. Between 2010 and 2023, the sheriff's office submitted evidence to the Santa Clara County crime lab and the Serological Research Institute for advanced DNA testing.
A DNA match was not found until 2024. Detectives identified 67-year-old Oscar Bolanos as a suspect in Pangborn's killing and sexual assault.
According to the sheriff's office, Bolanos was arrested in Los Angeles County in 1992 and was later convicted of sexually assaulting a juvenile. Deputies said Bolanos' DNA was collected and entered in law enforcement databases.
Following his release from state prison in 1994, Bolanos was deported to El Salvador. He had originally entered the U.S. in the early 1980s on a work visa.
Detectives worked with the Department of Justice, Department of Homeland Security and the FBI to determine his whereabouts.
Investigators determined that there was no record of Bolanos returning to the U.S. after his deportation. Salvadoran authorities found Bolanos near the same village he had listed on his original visa application.
Sonoma County detectives presented the case to the District Attorney's office, obtained an arrest warrant for murder and began working with the El Salvador government to arrest and extradite Bolanos.
Before authorities could take Bolanos into custody, he was found dead inside his home. Investigators learned that he was battling cancer and he had appeared to have died of natural causes, according to the sheriff's office.
"Although Bolanos will not face prosecution in court, the Sonoma County Sheriff's Office has concluded that the evidence establishes he sexually assaulted and murdered Robert Pangborn," deputies said in a statement.
The sheriff's office said it has about 70 open cold case investigations, with cases dating back to 1967.
