A San Pablo woman and her boyfriend were charged Thursday with murdering the father of her three children in a violent bid to gain custody, a prosecutor said.

Alicia Ortez, 35, and Amador Ortiz, 30, may have each pulled the trigger of a shotgun, killing 43-year-old Oscar Anguiano in his backyard Sunday night, said Mary Knox, a Contra Costa County prosecutor.

The victim's children - a 6-year-old girl and two boys, 12 and 3 - had been in bed but were jarred awake by the sounds of arguing. "In varying degrees, (they) saw or heard the events," including their father's screams, Knox said.

Now, the children are essentially orphaned, Knox said.

"These children have the potential of losing both parents, and they've been through an incredibly traumatic experience," Knox said. "Their father is dead, and their mother is in jail, accused of killing him."

Ortez and Ortiz were each charged with murder and abducting a child from his or her custodial parent, and Ortiz also faces a weapons enhancement. Both are being held in lieu of $1 million bail.

The violence unfolded about 11 p.m. Sunday as Anguiano watched a soccer game on television at his home on the 1600 block of 16th Street. Earlier that evening, he and his children had enjoyed a barbecue, Knox said.

Ortez and Ortiz arrived at the home in a Honda Accord that Ortiz had stolen in hopes of avoiding detection, the prosecutor said. The two were allegedly armed with a shotgun Ortiz had recently purchased.

Witnesses told police they heard "two male voices and a female voice, arguing in Spanish" before two shots rang out, Knox said.

Anguiano, who worked as a mechanic at a Mill Valley auto body shop, was shot twice in the chest at close range, authorities said. His body wasn't found until the following morning. Police issued a statewide alert when they couldn't find Ortez or her children.

Officers later arrested both suspects and recovered the shotgun at the Richmond home of Ortiz's parents, authorities said.

Ortez and Anguiano had a contentious relationship, according to Contra Costa County court records.

In November, Ortez was granted a temporary restraining order against Anguiano after she accused him of hitting her on the head, throwing her to the floor and threatening to kill her. In court filings, Anguiano said Ortez was undependable and was often late picking up the children. A judge ordered that the two share joint legal custody, while awarding primary physical custody of the children to Ortez.

Earlier this year, the judge denied a request by Anguiano for sole custody. According to Knox, though, people close to Anguiano said he had been granted sole physical custody, and was his children's primary caregiver, because of drug abuse by Ortez.

Witnesses told police that Ortez had in the past threatened to kill her children, or herself or Anguiano if she didn't win custody of her children, Knox said.