Christopher Shumey had the barrel of a shotgun in his mouth, with his finger on the trigger, when he heard his mother walk up to his front door, a defense attorney told a jury Monday.

After his mother knocked, Shumey turned the gun toward the door and — in “an act of insanity,” defense attorney Pierre Blahnik said — he fired.

“Christopher Shumey loved his mother, and he would never do anything to harm her,” Blahnik said, then added, “if he was in his right mind.”

But Deputy District Attorney Karen Gray argued that Shumey knew exactly what he was doing when he gunned down his mother, Karen Shumey, in San Luis Obispo on Sept. 17, 2011.

“He felt she was smothering him, trying to control his life,” she said.

During opening statements in Shumey’s murder trial, attorneys presented two contrasting portrayals of the 36-year-old defendant, who appeared to doze off at times during Monday’s session.

Blahnik said Shumey was a mentally disturbed person, who heard the disapproving voice of God, saw dragons that weren’t there and wrote nonsensical letters to celebrities. Gray said Shumey was a college graduate who was coherent and acting normally both before and after his shot his mother, a 65-year-old teacher at Vandenberg Middle School in the Lompoc Valley.

Both attorneys agreed that Shumey’s mother was trying to help her son when she was shot two times. She and her son had eaten dinner together the night before. Yet, when she returned the next day to help him prepare paperwork for disability, the two bickered.

Shumey said they agreed that she would leave the house for 20 minutes so he could cool down. The attorneys disagreed on what happened next.

“When she left, he got the shotgun because he wanted to kill someone,” Gray said.

When Karen Shumey returned, her son fired one shot through the door, hitting his mother in the back. After she screamed, he reloaded, opened the door and fired again, this time aiming at her head.

“Then the screaming stopped,” Gray said.

Later, Gray added, Shumey told police, “I wanted her to die, so I shot her” and “I didn’t care” that she was scared after getting shot the first time.

But Blahnik said Shumey’s original intent was to shoot himself — as he’d predicted he would do in a composition book that investigators uncovered.

“But, try as he might, he just could not will himself to pull the trigger,” said Blahnik, who will argue that his client was legally insane at the time of the shooting.

Shumey’s mental problems began, Blahnik said, when he was a senior at UC Santa Cruz in 1999.

“He was hearing command hallucinations from God and seeing things that weren’t there,” he said.

Shumey was sent to mental hospitals on multiple occasions, Blahnik said, and he would eventually be diagnosed with schizoaffective disorder.

While he had seemed to stabilize and worked at local wineries for eight years, he began to regress in March 2011, Blahnik said. He abruptly quit his job in August and wound up at Cottage Hospital in Santa Barbara at the end of the month for treatment of mental health issues.

His father had wanted him to stay longer, Blahnik said. Less than two weeks after Shumey’s release, his mother was dead and he was charged with murder.