CENTENNIAL – A jury in Arapahoe County has reached a decision after deliberating only six-and-a-half hours over the fate of the gunman who killed 12 and injured at least 70 others in an Aurora movie theater in July 2012.

The jury reached their verdict at 2 p.m. After a three-hour warning in order for victims' families to make their way to the Arapahoe County Justice Center, Judge Carlos Samour read the verdict. The verdict was read at 5 p.m.

The jury of 12 could not reach a unanimous decision, so the court automatically sentenced James Holmes to life in prison without the possibility of parole.

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To have reached this decision, it means all members of the jury could not unanimously agree the gunman should be sentenced to death.

On Aug. 3, the jury reached a decision in what is known as "phase two" of the gunman's sentencing.

They determined the mitigating factors presented by the defense did not outweigh the aggravating factors presented by the prosecution during phase one of sentencing.

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With that decision, the jury left the option for the death penalty on the table. Had they decided there were mitigating factors based on testimony from the theater shooter's friends and family, the gunman would have been sentenced to life in prison automatically.

Victim impact testimony began Tuesday, Aug. 4, wrapping up on Thursday, Aug. 6. During this phase, the prosecution called family members of the 12 victims to testify.

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The defense and the prosecution presented their final closing arguments on Thursday, Aug. 6 and later that afternoon, the case went to the jury for the final decision in how to sentence the gunman.

BLOG: Aurora theater shooting final sentencing phase blog: Day 3
BLOG: Aurora theater shooting final sentencing phase blog: Day 2
BLOG: Aurora theater shooting final sentencing phase blog: Day 1

In summary, the jury had to determine if the defense's plea for them to spare the defendant's life outweighed the prosecution's argument for his execution.

James Holmes was found guilty on July 16, 2015 for killing 12 and wounding at least 70 people in an attack at an Aurora movie theater on July 20, 2012. His defense team had argued Holmes was insane at the time of the attack, and had the jury found he was, the death penalty would have been off the table.

Read more from 9NEWS' Aurora theater trial coverage here.

(© 2015 KUSA)