The trial of confessed Colorado theater shooter James Holmes begins Monday.

Prosecutors say that Holmes, who is charged with killing 12 people and injuring 70 more in the July 2012 attack, was sane and will ask jurors to convict him and sentence him to death, while defense attorneys say that he is not guilty by reason of insanity.

Judge Andrew Napolitano shared insight on "America's Newsroom" on how this defense shifts a heavy burden of proof to the prosecutors.

"Not only do they have to prove that he did it, they have to prove beyond a reasonable doubt that he was sane," Judge Nap said. "That's the highest level of proof there is."

Judge Nap explained that if this case was taking place in a state like Texas, then the burden would be on the defense to prove that Holmes was insane.

Judge Nap said that Holmes' offer to plead guilty by reason of insanity - and spend the rest of his life in a mental institution - has been rejected by the state because they want to execute him due to the horrific nature of his crimes.

"Legal insanity means a mental defect so strong and overbearing that he didn't know right from wrong," Judge Nap explained. "It's really a very, very difficult standard to put premeditated behavior into that box. And the more premeditated behavior there is, the easier it will be for the state to prove sanity."

Judge Nap revealed that the prosecution also faces another hurdle. If the jury rejects the insanity defense but believes that Holmes is "mentally deficient," then he will be sentenced to life in a mental institution.

"Something he has offered to do $7 million tax dollars ago, spent by the state of Colorado, which is also funding his defense," Judge Nap said.

Watch more above.

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