MENDOCINO COUNTY, Calif. — The Mendocino County Sheriff’s Office (MCSO) responded on Monday to social media posts from a woman who alleged her father, Jon Charles Trefil, is a serial killer.
The MCSO said they began investigating the allegations in Jan. 2023, when detectives from the Sheriff’s office said they met with an advocate of Trefil’s daughter after she reported the allegations to various local and regional law enforcement agencies. That advocate then helped detectives speak with Trefil about the alleged crimes.
Recordings, scanned journals, and other investigative materials were shared with officers, they said, which resulted in an investigation into the claims.
Investigators later met with Trefil’s daughter in Feb. of 2023, who said her father spoke about murdering several people from the 1970s through the 1990s. Trefil’s daughter also provided a long written statement, which was retained as evidence.
According to the MCSO, Trefil’s daughter said her father spoke about these killings as the two of them spent time together with the advocate, which led her to begin researching unsolved murders in Mendocino County and to suspect her father was responsible for a murder in the area in the 1970s. According to his daughter, Trefil ultimately admitted to a murder in the area during that time.
Detectives from the MCSO also obtained pictures, copies of journal entries, and recordings from the meetings between Trefil, his daughter, and the advocate.
Detectives said they researched the unsolved case Trefil admitted to and compared the information his daughter provided to the facts of the case. They found several items from the case submitted for DNA analysis in 2006 to the Department of Justice (DOJ), which resulted in a DNA source for an unknown male. Detectives determined there were some consistencies in the information provided by Trefil’s daughter and the unsolved case, so they sought a warrant to obtain Trefil’s DNA for comparison to the evidence found in 2006.
A search warrant was authorized by a Mendocino County judge in May 2023 and the DNA sample from Trefil was submitted to the DOJ. Detectives later received a report stating that Trefil’s DNA did not match that of the unknown subject from the unsolved case. They said Trefil’s DNA was then loaded into CODIS for regular comparisons to DNA profiles uploaded from unsolved cases.
The MCSO said they have never been informed that Trefil’s DNA Profile matched or potentially matches any evidence submitted into the system.
Detectives said Trefil’s daughter also alleged her father buried numerous people he claims to have murdered at a cabin in Comptche, CA. Officers searched the property and cabin but did not locate remains or other evidence to verify the claims. The MCSO said Trefil’s daughter claimed that he referenced other serial killers, but said these claims were found to be unsubstantiated as well.
Detectives scanned Trefil’s diaries and journals and found no confessions to any murders.
Officers have not interviewed Trefil directly due to his fragile medical condition and statements from his family that he will not cooperate with officials. The MCSO added that they will continue investigating the crimes when legally justified by probable cause.
