Marin Sheriff's Deputy Killed in Petaluma Double Domestic Homicide

An off-duty Marin County sheriff's deputy was shot and killed early this morning by the ex-boyfriend of a female friend during a domestic violence incident near Petaluma, Assistant Sonoma County Sheriff Lorenzo Duenas said.

The incident was reported at about 12:15 a.m. at a home in the 800 block of Liberty Road.

Investigators believe the deputy, Jim Mathiesen, 49, was killed by 28-year-old Thomas Edward Halloran before Halloran was fatally shot by a third man at the home, Duenas said.

Mathiesen, who had been a deputy for nine years, was friends with a female resident of the home on Liberty Road who had been dating Halloran since March, Duenas said.

Duenas said the relationship was rocky, and that Halloran had sent
death threats by phone and over the Internet to the woman after she broke off the relationship nine days ago.

Mathiesen had helped the woman, a family friend, in the past with her troubles with Halloran, and he went to the Liberty Road house after Halloran texted her a death threat around 11:30 p.m. Monday, Duenas said.

Halloran then showed up at the house. The fatal confrontation occurred when Mathiesen went outside the house to try to calm Halloran down, Duenas said.

Halloran shot Mathiesen twice in the upper torso, and Halloran's ex-girlfriend fled, Duenas said.

Halloran then allegedly took another woman who was living in the house hostage and forced her into a car, Duenas said.

Another male who was living in the house then shot Halloran in the leg and upper torso in defense of the female hostage, Duenas said.

Mathiesen and Halloran were both pronounced dead at the scene.

Halloran was on parole for making threats in the past against other victims, and the Sonoma County Sheriff's Office is investigating whether he had gang ties or affiliations, Duenas said.

"He had numerous arrests in Marin and Sonoma counties," Duenas said.

Both weapons used in the shootings were recovered, Duenas said

Halloran's ex-girlfriend is safe, and is being interviewed by sheriff's investigators, Duenas said.

Bay City News