Sean Janssen, The Union Democrat

Philip Marshall acted alone in killing his two teenage children, a pet Shih Tzu and himself after a history of mental illness and a messy split with the children's mother, according to a six-page report released Friday afternoon by the Calaveras County Sheriff's Office.

The report details the investigation that took place after the bodies of all three family members were discovered Feb. 2 at the Marshall's Forest Meadows home.

The Sheriff's Office investigation concluded Marshall shot his son Alex, 17, and daughter Macaila, 14, as they slept on the living room couch before turning the 9mm Glock semiautomatic handgun he purchased in 2011 in Turlock on himself.

Toxicology test results showed both children had moderate levels of alcohol in their system at the time of their deaths, with Macaila registering a .05 blood-alcohol content and Alex a .03. In addition, Macaila had apparently taken diphenhydrameine, an over-the-counter antihistamine and sleep aid, commonly sold as Benadryl.

Philip Marshall's toxicology screen showed painkillers hydrocodone and morphine in his blood as well as hydroxybupropion, an antidepressant.

Investigators looked at Marshall's medical records and determined he had been diagnosed with bipolar disorder.

A lengthy history of run-ins with wife Sean Plummer, the children's mother, is documented dating back to 2008, when she began divorce proceedings, only to later withdraw the petition and reinstate it in October 2012.

On Nov. 11, 2008, Plummer's sister, Erin Chamberlain, then a Murphys resident, told police Marshall threatened Plummer she "will not see December." Eleven days later, Chamberlain said she felt threatened "for the safety of her children" as Marshall repeatedly drove past her home. Phone messages Marshall left at Chamberlain's home in December included statements that "if you don't call me, mom is going to have problems, we don't want this," "Sean, you are going to get what's coming to you" and "Macaila, this is daddy. We are going to have lunch. We need to talk right now. If not, something is going to happen." On Dec. 7, the report states Marshall violated an emergency protection order.

On Jan. 27, 2013, the report stated Marshall purchased a distinctive type of Fiocchi 9mm ammo from Big 5 Sporting Goods in Sonora, confirmed by a review of surveillance video at the store. The ammunition company later donated some of the same ammunition for a ballistics test at Marshall's home investigators used to conclude it was possible for the shots to be fired without neighbors hearing them.

"During the multiple tests the detectives found that it took an average of a total of two seconds to shoot each victim, demonstrating that it was possible to shoot both children prior to one of them waking up," the report stated. The home had been unlocked with no signs of forced entry when investigators arrived and valuables remained in plain sight, according to the report. A safe was left open with a handwritten note on a medical marijuana recommendation card that read "Hi Sean!"

"There was no evidence to support a theory that anyone else could have committed this crime, or that any other persons were present at the time of the shootings. Macaila and Alex Marshall both appeared to be sleeping at the time they were shot, indicating no signs of a struggle with a possible intruder. There was no evidence of a struggle with Phillip Marshall, and no signs of forced entry into the home," the report concluded. "Various items of value were still present inside the home, and no evidence of any additional weapons was found.

Lastly, there was no evidence that Phillip Marshall or his children were moved or repositioned after the shooting, which would indicate an altered crime scene. Based on the final findings of the investigators, evidence shows that Philip Marshall, and not an outside fourth person, shot and killed Macaila, Alex, the family dog, and then himself. To conclude, it is determined that this case was a double murder-suicide."

A detailed report on the investigation's conclusions will appear in Monday's edition of The Union Democrat.