Minutes before she was shot to death, Karen Shumey sat in her car and cried as she talked to her husband on the phone. From her parking spot she could see the San Luis Obispo apartment where she’d just had an argument with her son.

As she prepared to return to that apartment, her husband, Robert Shumey, asked if she was afraid of their son, Christopher Shumey.

“She said, ‘No, I’m not afraid to go back — I’m afraid of what I’ll find,’ ” Robert Shumey testified during his son’s murder trial Thursday, later adding, “Chris was becoming so depressed.”

In what amounts to a preview of the Superior Court trial’s second phase — to determine whether Christopher Shumey was legally insane when he shot his mother — defense attorney Pierre Blahnik called several of Shumey’s relatives to the stand. The unusual move — survivors of a murder usually don’t testify for the defense — was intended to show that the defendant’s mental illness led the suicidal Shumey to kill his mother on Sept. 17, 2011, just outside his apartment.

The District Attorney’s Office will argue that Shumey, 36, knew what he was doing and felt his mother was being overly controlling when he shot her two times with a 12-gauge shotgun. His calm and articulate demeanor afterward, prosecutors think, helps prove it. But Blahnik will point to Shumey’s history of mental illness, first documented when he was a senior in college in 1999.

It was in the spring of that year, Robert Shumey said, that he and his wife began getting strange calls from their son. When they drove to Santa Cruz, where he was attending school, they noticed he had lost weight and was at times non-communicative.

“He looked like he was staring off into space,” said Robert Shumey, a real estate appraiser from Arroyo Grande. “A couple of minutes later, he’d be OK.”

Eventually, Christopher Shumey would be diagnosed with schizoaffective disorder, a mental condition that causes both a loss of contact with reality (psychosis) and mood problems.

“We went through a whole battery of medications, and the personality changed several times,” the defendant’s father said.

Before the mental illness set in, family members said Christopher Shumey had a happy childhood with a close-knit family.

“Chris has been a great brother,” his brother Bryan Shumey said.

Karen Shumey’s sister, Pamela Harris, said her sibling had a “loving, playful, close” relationship with Christopher Shumey. When she gathered personal items from Christopher Shumey’s apartment after the shooting, she said, she found framed photos of his mother.

All of the relatives, including Harris’ husband, told the jury that Christopher Shumey was a non-violent person.

“There was never any violence,” his brother testified. “Chris is just a very fragile soul and always has been.”