As she ran out the door after hearing gunshots fired from the garage of her Upper Marlboro home, she came eye-to-eye with her eldest son, the gun still smoking in his right hand.

The grandchildren were crying. She was yelling, “What did you do?”

And her husband lay bleeding in the next room.

“I can’t believe my husband is dead,” Bernadette James-Newell screamed, her wails captured on a recorded 911 call. “I can’t believe my son did this to me!”

Two years later, James-Newell testified in court that it was, indeed, her son, Antwan James, who fired the gun. But, she said, he was not the man she knew and raised.

“It was a demonic spirit on him,” James-Newell said. “It wasn’t my son.”

A Prince George’s County jury Tuesday convicted James, 30, of manslaughter in the 2013 killing of his stepfather, Joseph Newell, 46. It was an emotional case that divided a once blended family and placed James-Newell in the difficult position of testifying against her son — a former D.C. firefighter — in the slaying of her husband — a homicide detective for D.C. police.

“In one fell swoop, the defendant took out his stepfather and brought his mother to her knees,” Deputy State’s Attorney Donnell Turner told the jury. “Her husband was killed essentially in front of her eyes, but then she came in here . . . and she was trying to protect her son.”

Prosecutors and the defense agree that James shot his stepfather. But the trial that started last week centered on whether James was coherent enough to deliberately shoot Newell or whether he was so intoxicated that he was unaware that his actions could be fatal. If a jury found he knowingly fired, as prosecutors argued, he would be convicted of murder instead of involuntary manslaughter, which carries a lighter sentence.

The case stems from the evening of April 22, 2013. Newell had come home from work and asked his two stepchildren and his wife’s great-nephew to help him with yardwork, according to court testimony.

James did not get up to help, and after about 15 minutes of arguing with James-Newell, she issued an ultimatum: help her husband or “get the hell out” of the house.

That is when James went after his stepfather, prosecutors said.

“ ‘You’re only doing this because of him,’ ” James-Newell recalled her son yelling. “ ‘Watch this.’ ”

Video played during the trial showed Newell standing on a ladder in the driveway of the family’s brick home changing a lightbulb when James approached and shot the 22-year D.C. police veteran — 18 times. Newell was in house slippers and his work clothes when he fell face down onto the concrete.

“I imagine that every day that he went to work as a homicide detective, he prayed that he came home safely,” Turner said. “How ironic it is that Joseph Newell died while he was at home.”

But despite the video evidence of the gunshots that all struck Newell at point-blank range, Thomas C. Mooney convinced the jury that his client did not know what he was doing. Mooney argued that James suffered from severe depression after working for the D.C. fire department. He watched pregnant women give birth to stillborn babies, James-Newell testified. And he saw people burned and severely injured, according to his attorney. He was so distressed that he stopped bathing, stayed in his room and drank heavily, witnesses and Mooney said.

That emotional toll exploded with the shooting, Mooney said. James had smoked synthetic marijuana earlier in the day and consumed tequila, gin and two kinds of vodka.

The argument with his mother, the shrieking children and the liquor created a “perfect storm” that caused James to snap, Mooney said.

“This case is about someone who had given up and who was self-medicating,” Mooney said. “It came on the heels of . . . a number of factors in that young man’s life that was a toxic mess.”

Prosecutors, however, argued that James was not that drunk. He was able to play the keyboard at a friend’s recording studio, drop off and pick up his child from day care and chat with his brother about getting a commercial drivers license, witnesses testified.

“He was not too drunk to tell his mother, ‘Watch this,’ ” Deputy State’s Attorney Carol A. Coderre told the jury.

On the witness stand, it was clear that James-Newell was torn. A judge had to warn her to answer prosecutors’ questions directly. Whenever prosecutors asked questions that may have put her son in a negative light, she added caveats: “He wasn’t himself,” or “That wasn’t my son.”

The courtroom was packed with dozens of relatives: James’s family on one side, Newell’s on the other. Relatives gasped, cried and rolled their eyes at various points in the trial.

When the jury announced its verdict, James’s family praised God and breathed sighs of relief, while members of Newell’s family shook their heads in disappointment.

State’s Attorney Angela Alsobrooks said that she respects the jury’s verdict, but she thought the decision was surprising and unjust. Had the jury handed down a first-degree murder conviction, James could have faced up to life in prison. With involuntary manslaughter, the most prosecutors can ask for is 10 years.

“The jury in this case rejected the evidence, and they sympathized with the mother,” Alsobrooks said. “This was a videotaped execution, and it was unprovoked in so many ways.”

After the trial, James-Newell stood firm. Her son was not in his right mind when he fired.

The families will meet again in November, when James is scheduled to be sentenced.

Until then, James-Newell said that she will continue to mourn her “best friend.”

“I wouldn’t want anybody, not even my worst enemy, to bear the pain that I had to carry for my son and for my husband,” she said.