Mathiesen, a nine-year sheriff's office veteran, went to the residence unarmed and off duty late Monday night after Halloran's ex-girlfriend notified him Halloran had texted death threats to her. Mathiesen was a close friend of the woman and her family.
One of those family members then shot and killed Halloran after Halloran shot Mathiesen twice in the chest and took a woman hostage in a garage at the residence.
Sonoma County Superior Court records show Halloran was arrested on July 22, 2008, for threatening a crime with intent to terrorize.
Petaluma police said at the time that Halloran vandalized his ex-girlfriend's car and sent her death threats via text messages. Marin County sheriff's deputies arrested him two days later and turned him over to Petaluma police.
Halloran pleaded no contest to the felony threat charge on Aug. 18, 2008. Judge Elliot Daum indicated he would sentence Halloran to a probation term if he entered a drug treatment program.
The judge also vacated a criminal protective order and allowed Halloran to have peaceful contact with the victim.
On Sept. 16, 2008, Daum sentenced Halloran to three years' probation and one year in Sonoma County Jail. Daum said the sentence could be served in any penal institution.
The judge ordered him not to possess any weapons or alcohol or take steroids, and he ordered Halloran to complete a 52-week batter's program.
Halloran was cited on Jan. 21, 2009, for violating his probation. On Feb. 5, 2009, Sonoma County Superior Court Judge Dean Beaupre ordered him released from Marin County Jail so he could enter a drug treatment program.
Court records show Halloran violated his Sonoma County probation again in June and August 2009.
In November 2009, Halloran admitted he failed to complete the residential drug treatment program and did not enroll in a batter's group. He was ordered to enroll in the Salvation Army's residential treatment program in San Francisco.
His probation was revoked again on June 8, 2010. On July 15, 2010, Halloran was convicted of the probation violation and was sentenced by Judge Rene Chouteau to two years in state prison for the threat charge. He had 480 days credit for time served and was paroled in November 2010.
Deputy Public Defender Jeff Mitchell, who represented Halloran during many of his Sonoma County court proceedings, said the probation violations "were minor violations" for not completing drug treatment or batter's programs.
"There was nothing earth shattering. There were frustrating, repeated dealings with him. I never got the feeling he would do something like this. He was fixated on (sending) text messages and phone calls. A lot of guys get possessive and obsessive, but they don't shoot people," Mitchell said.
Halloran also pleaded guilty in May 2008 to a misdemeanor vandalism charge and received three years' probation. He was convicted in October 2006 of possession of a controlled substance.
His most recent Sonoma County court appearance was on June 13, when he was given two years' probation for possessing a prescription medication by fraud on May 5. A burglary charge against him was dismissed.
The Marin County Deputy Sheriff's Association today announced it has established a trust fund for Mathiesen's wife and two sons.
Donations may be sent to the Mathiesen Family Trust in care of the Marin County Federal Credit Union, 30 North San Pedro Road, Suite 115, San Rafael, CA 94903.
Tax-deductible contributions also may be made to Meals on Wheels of America, Development Department, 203 S. Union St., Alexandria, Va. 22314. Hugh J. Baker, president of the Marin County Deputy Sheriff's Association, paid tribute today to Mathiesen.
"Helping someone in need was Jim's persona," Baker said. "I can't count the number of times Jim sacrificed his own money, sleep or time off to help someone who needed something."
Baker said the ex-girlfriend and her family called Mathiesen "because they knew he was a peace officer and they knew he would know what to do."
"Jim died as he lived, reaching out to someone in need. He had a heart of gold, solid gold," Baker said.