Bret Matz, 46, is being held under no bail in the Sonoma County jail. A preliminary hearing date will be set on Feb. 9.
The Sonoma County Sheriff's Department said a woman contacted the Monte Rio Fire Department on Jan. 2 and said a man, later identified as Matz, had just left her business after telling her he killed his roommate.
The business owner told fire personnel Matz was last seen walking adjacent to the fire department toward Starrett Hill.
Fire department staff soon spotted Matz near the fire station leaning over a roadside guardrail on Middle Terrace Road, and contacted him, believing he was in distress, according to the sheriff's department. He allegedly then told fire personnel he had killed his roommate.
A fire department employee walked to Matz' home and forcibly entered the residence to check on the roommate's welfare. The body of 46-year-old Guess was found inside.
Guess appeared to have been struck multiple times in the head with a blunt instrument. Fire personnel remained at the home with Matz and summoned sheriff's deputies.
Matz had been arrested for a domestic violence incident involving Guess in September but the case was dismissed after Guess asked that a criminal protective order be revoked.
Matz pleaded no contest Dec. 5 to separate misdemeanor charges of vandalism and disorderly conduct stemming from an Aug. 14 incident. He received a two-year conditional sentence.
He also received a three-year conditional sentence after pleading no contest Dec. 5 to a May 18 misdemeanor DUI.