AURORA, CO — (CNN) If only she’d known, Arlene Holmes said. If only her son’s psychiatrist had said something about the bad, scary things going on inside his head, she could have done so much more.

“I would have been crawling here on all fours,” Holmes told a jury tasked with deciding whether her only son lives or dies. “None of this would have happened.”

“This” is one of the worst mass shootings in recent U.S. history. And 27-year-old son, James Eagan Holmes, someone she always thought of as a good boy, stands convicted as the shooter.

But, in a phone call a month before the theater shootings, psychiatrist Lynne Fenton didn’t say a word to Arlene Holmes about the homicidal thoughts her son had voiced. She said nothing about her belief that he might be psychotic.

“She didn’t tell me. She didn’t tell me. She didn’t tell me,” Holmes said, breaking into tears on the witness stand as her son looked on, rocking gently in his chair.

“We wouldn’t be sitting here if she’d told me that.”

All the psychiatrist said when she called on June 11, 2012, was that her son was dropping out of his graduate course in neuroscience at the University of Colorado’s Anschutz Medical Campus.

“She said she saw him for social anxiety, and he had come to her for this problem,” Arlene Holmes recalled. “She said, ‘Did you know he quit school?’ I said I suspected it because he was struggling.”

With the limited information she had, all she could do was offer to pay for her son’s sessions with the psychiatrist after his student insurance ran out. “I said, ‘we work, we have money. We can pay for it.’ She said that would be fine.”

She never again heard from Fenton.

Five weeks later, James Holmes burst into a crowded movie theater, armed to the teeth and wearing body armor. He tossed a tear gas canister and then fired into the crowd, using three guns. Twelve people died and 70 more were wounded.

A jury has convicted James Holmes of 24 counts of capital murder — two counts for each person slain — and is now deciding whether the former doctorate candidate should receive the death penalty.

“We don’t kill people for being sick,” defense attorney Rebekka Higgs said in her opening statement. It is the heart of a defense effort to persuade the jury to show mercy and recognize the role that James Holmes’ mental illness played in the crime.

Three dozen witnesses have testified during the so-called mitigation phase, including James Holmes’ parents and sister. Jurors could begin their deliberations as soon as Thursday afternoon.

The defense witnesses painted a picture of an exuberant boy, described by one teacher as a “Renaissance child,” who grew into a bright but nerdy teen and then a socially withdrawn adult.

Looking back, his mother says, she can see how her son changed as he began adolescence just before the family moved from Northern California to San Diego.

Once quick and skilled at soccer, he became uncoordinated and spent most of his time playing cards and video games.

“He was living on a blue note,” she said. She added that she felt guilty about her son “losing his joy.”

But despite the worry and the trips to counselors, she never thought he could be seriously mentally ill. Sure, she worried about the way he isolated himself from people. But he didn’t get in trouble, he wasn’t mean and he did well in school. “I thought I had a good kid,” she said.

She just assumed he was painfully shy. Other family members shared that trait.

“We never thought it was something like schizophrenia,” she said.

Higgs asked the question everyone in the room was thinking: How can that be?

“He was the most responsible person I know,” the mother replied. “I knew my own son. He managed his own finances. He went to school every day. He did all his chores without being told. He never harmed anyone, ever, until July 20, 2012.”

The Holmes family did not indulge in lengthy discussions about their feelings, both parents acknowledged. Indeed, they didn’t talk much at all. Arlene Holmes said she taught her children as she was taught — “Be stoic, don’t complain, don’t be weak.”

Instead, they kept James and his sister, Chris, busy with school, sports, music lessons, vacations, trips and other activities.

When their son attended college, and then graduate school, they stayed in touch through email. He never was one to talk on the phone. But, Arlene Holmes said, during the first months of 2012, his emails grew shorter and less frequent.

“I didn’t realize that his loudest cry for help was his silence,” she said.

They did talk on Mother’s Day and on July 4. At that time, he was well into the process of building his arsenal and planning the movie theater attack.

She had no inkling of what was to come just days later.

“When I heard, I asked myself, ‘How does he even know how to use a gun?’ ” There had never been guns in the house. “I was shocked that he used a gun.”

She was shocked again by what she saw the first time she visited her son at jail after his arrest. His hair was dyed bright red. He wore jail scrubs and shackles.

His eyes were darting all over the place, and “he had trouble finding each and every word.”

She attended all his court hearings and all but a couple of days of the trial, which was in its 59th day Wednesday. She made the journey from San Diego to Denver just so she could sit in the same room with him. She was glad to see he appeared to be looking at her as she testified.

She has seen him only two other times in jail, but she has mailed him dozens of letters with photographs taken during his childhood. She wants to maintain a connection with him, so he won’t forget the happy child and top student he used to be.

She wants to keep writing him, and perhaps even visit him if he’ll allow it.

“People say to me that when your kid turns 18, you’re done,” she said. “It’s not true. We’re not done. We’re never done, and that’s why we’re sitting here. We’re not done.”

Defense attorney Higgs asked Arlene Holmes whether still loves him, despite everything that has happened.

“I still love my son, yes,” she said.

Why?

“Because I understand he has a serious mental illness. He didn’t ask for that. Schizophrenia chose him; he didn’t choose it.”

And then, crying, she said it again: “I still love my son. I still do.”

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