Jurors in the Aurora Theater shooting trial will begin deliberating the fate of James Holmes on Thursday to decide whether he should be sentenced to life in prison or death.

Holmes' attorneys say that the 27-year-old mass murderer was clinically insane when he opened fire at an Aurora movie theater showing "The Dark Knight" on July 20, 2012. As a result, 12 moviegoers were killed, while 70 others were injured.

According to the defense, the shooter suffers from schizophrenia and could not tell right from wrong when he intentionally killed people at the movie premiere. Therefore, they argued he should not be found culpable.

However, a jury rejected his insanity plea and convicted the former neuroscience graduate student for murder earlier this month. Now, the jurors will decide whether to sentence him to the death penalty or life in prison without parole.

On Wednesday, the shooter's mother, Arlene Holmes, pleaded for the jury to spare her son's life while testifying about his relatively happy and average life before the shootings.

"He was the most responsible person I know. 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," she said, according to CNN.

She said that she was shocked to learn that her son had committed a mass murder because he had never even used a gun -- there had never been guns in the house.

"When I heard, I asked myself, 'How does he even know how to use a gun?' I was shocked that he used a gun."

She said that she would like to continue to write him letters and pay him visits, if he approves.

"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."

Arlene added, "Schizophrenia chose him. He didn't choose it. And I still love my son. I still do," reports ABC News.

The killer's father, Bob, also testified on the witness stand, telling the court that his son was an "excellent kid."