Matt Magee surrendered without incident to the Pearl River Police Department on Tuesday, June 20, 2017.

Matt Magee was raving mad when he showed up at his ex-wife's trailer home in Pearl River in June 2017, convinced that Jennifer Wallace Magee had introduced their children to the man she was dating, breaking a pact they had made.

But Magee didn't show up there just to confront his ex-wife: He intended to kill her and her boyfriend, Donald Gros.

That's the account that Assistant District Attorney Blair Alford laid out for the jury Tuesday in opening arguments at Magee's trial in 22nd Judicial District Court on two counts of first-degree murder.

"The defendant developed specific intent to take the lives of Jennifer Wallace Magee and Donald Gros for no other reason than he was mad," Alford said, painting a picture of a failed marriage, an ex-wife who was moving on and an ex-husband who was struggling with that reality.

The flashpoint came when the couple's young son, who was talking on the phone with his mother from his father's truck, asked to speak to "Mr. Donald," Alford said.

Soon after hearing that, Matt Magee dropped his children off at the home of his mother and stepfather without explanation, then drove to his ex-wife's house, opening fire on Gros. Bullets penetrated his shoulder, neck and head with what Alford described as "military precision."

Magee then turned the weapon on his ex-wife as she tried to run away, striking her in the back and in the head, Alford said.

Magee's attorneys, however, told the jury that their client did not commit murder and was in fact acting in self-defense.

He was afraid, not angry, said lawyer James Carrington. Gros had pulled a gun on Magee, who was arguing with his ex-wife about allowing the children to meet her boyfriend, Carrington said.

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Chaos erupted as the two men struggled over the weapon, with a bullet striking a fire extinguisher that spewed foam all over the trailer, Carrington said. Bullets also struck Jennifer Magee.

"He didn't go to Jennifer's trailer that night to hurt or kill her, or to fight her boyfriend, Donald Gros," Carrington said. "He went to speak to Jennifer about his children, the thing that meant more to him than anything in life."

Carrington also told the jury that testimony will show Gros had gunpowder residue on his hands.

Magee's stepfather, Tommy Cooper, took the stand Tuesday to testify about the events of that night and the call he made to 911.

Cooper said that Magee dropped the children off at his house but didn't follow them inside. Cooper said he checked in the driveway after about 10 minutes, but Magee's truck was gone.

Then the phone rang, Cooper said, and his wife answered, asking over and over again what had happened. He took the phone from her, he testified. It was Magee on the other end of the line.

"He said, 'I effed up.' I asked him, 'What is it?' He said, 'I shot her.' I asked, 'Who did you shoot?' He said, 'I shot Jennifer. I killed her.' "

Assistant District Attorney Collin Sims asked Cooper if Magee mentioned shooting Gros or getting into a fight with him. "Did he ever tell you he was afraid?" Sims asked. "No sir," Cooper replied to each question.

Cooper said his stepson told him to please take care of his kids and to tell them that he loved them and that he loved his mother.

"I said, 'Matt, if you run, they're going to kill you,' " Cooper testified.

On cross-examination, Cooper said that Magee told him not to worry about what the police would do, saying, "I'm going to kill myself."

But when the prosecution asked Cooper if he believed Magee was going to commit suicide, Cooper said no.

"Why not?" Sims asked.

"Because he's not that type," Cooper replied.

The trial, in Judge August Hand's court, is expected to last all week.

Follow Sara Pagones on Twitter, @spagonesadvocat.