Penalty phase begins in trial of James Holmes over Aurora theater massacre

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James Holmes says he won't testify for himself in the penalty phase of murder trial

He was convicted of killing 12 people in an Aurora, Colorado, movie theater

CNN  — 

The monthlong penalty phase of the trial of James Holmes, who could be sentenced to death for killing 12 people in a Colorado movie theater, began Wednesday morning with the judge giving instructions to the jury.

Holmes pleaded not guilty by reason of insanity, but the jury rejected that defense last week when it found Holmes guilty on 24 counts of murder and 140 counts of attempted murder.

His attorneys are expected to raise his mental illness again during the penalty phase when they try to persuade the same jurors to spare his life.

The prosecution has signaled it will seek the death penalty.

Holmes, a failed neuroscience graduate student, told Judge Carlos Samour on Tuesday that he will not testify for himself during the penalty phase. He said he voluntarily made his decision and was not pressured by his lawyers.

He didn’t testify for himself during the first phase of the trial either.

Holmes was found guilty of killing 12 people and wounding 70 others on July 20, 2012, when he opened fire in a crowded movie theater showing “The Dark Knight Rises” in the Denver suburb of Aurora.

It was one of the United States’ deadliest mass shootings.

The jury – nine women and three men – quickly rejected his insanity defense last week, finding that although he is a diagnosed schizophrenic, he knew what he was doing that night, and that it was wrong.

Prosecutors are expected to launch their case for execution by presenting powerful victim impact evidence from some of the 70 shooting survivors and grieving relatives of the people who died – victims whom Holmes told a psychiatrist he considered “collateral damage.”

Jurors will be asked to find aggravating factors and mitigating factors, and then to weigh them.

It is up to the defense to present evidence of mitigating factors – circumstances under which the penalty would be considered too harsh a punishment.

CNN’s Ann O’Neill, Sara Weisfeldt and Ana Cabrera contributed to this report.