Christopher Shumey wasn’t suicidal when he gunned down his mother, a prosecutor argued Friday — he was angry because his mother wouldn’t leave him alone.

“He was 36 years old and wanted to have his own life (without) her in it,” Deputy District Attorney Karen Gray told a jury.

But defense attorney Pierre Blahnik countered that his client’s suicidal intentions were indicative of his mental illness.

“This was suicidal rage,” Blahnik said.

After closing arguments, jurors began deliberating in the first phase of Shumey’s trial, in which they will determine whether he was guilty of first-degree murder of his mother.

According to trial testimony, Shumey had argued with his mother, eighth-grade teacher Karen Shumey, of Arroyo Grande, on Sept. 17, 2011, turning a table over in a rage. After his mother left so he could cool off, Shumey grabbed a 12-gauge shotgun. When his mother returned, he shot her once through the front door as she stood on a balcony. Then, as she screamed, he retrieved another slug from another side of his apartment, reloaded, opened the door and shot his mother again.

“The top of her head was found at the bottom of the stairs,” said Gray, who held the shotgun during a portion of her closing argument.

During the attorney’s arguments, Shumey whispered to himself and downed several cups of water, emptying a pitcher.

Blahnik said Shumey had planned to kill himself after the argument but inexplicably shot his mother instead. Later, Shumey told police, “I just can’t believe I shot her,” which, Blahnik said, was proof that he didn’t deliberately commit the crime.

If jurors don’t think he premeditated the crime, they can opt for a lesser charge of second-degree murder. He also faces a charge of assault with a deadly weapon on a peace officer for allegedly firing a shot at responding police.

Blahnik said the prosecution’s theory that Karen Shumey was crouched over and clutching her head when she was shot a second time was “sensationalistic.”

“It wasn’t this execution-style murder the people want you to believe it was,” he said.

But, Gray said, when Shumey took time to reload so he could shoot his mother again, it proved he methodically planned to kill her.

“She would have survived had he shown mercy on his screaming, terrified mother,” she said.

After the shooting, she said, Shumey was calm and callous, at one point telling police he wasn’t swayed by his mother’s screams.

“Where are the tears for his mother?” Gray asked. “Where’s the remorse?”

If Shumey is found responsible for the killing, Blahnik will attempt to prove he was legally insane at the time, pointing to mental health issues dating to 1999.

After multiple hospitalizations, his mental condition seemed to stabilize for several years. But before the killing, he began to slide, prompting his parents to keep a diary of his mental health. As his condition worsened, Shumey stole the shotgun from his father. Gray said bullet holes in his apartment before the killing show he was practicing how to shoot the weapon; Blahnik said they were signs of failed suicide attempts.

During the trial’s second phase, numerous psychiatric witnesses will testify for both the defense and prosecution.