Aurora movie theater killer James Holmes' parents wrote a letter begging for prosecutors to spare the life of their son who they say is mentally ill.

Holmes was found guilty in connection with the 12 moviegoers he fatally shot at a suburban Denver movie theater in July 2012. Evidence presented at trial showed the killer methodically planned his attack - he bought an assault rifle, shotgun, two semi-automatic pistols, more than 6,000 rounds of ammunition, bomb-making material and other gear for nearly two months before the shootings, reported USA Today. Holmes also had pictures in his cell phone that proved he staked out the rear of the theater and exit doors before the shootings.

Holmes' parents are pleading that their son be locked up for life, instead of executed, because he is mentally ill. He underwent two medical examinations that remain confidential, reported USA Today. 

"We realize treatment in an institution would be best for our son. We love our son, we have always loved him, and we do not want him to be executed," Robert and Arlene Holmes wrote in a letter distributed to Denver media Friday morning. "We also decry the need for a trial. A lengthy trial requires everyone to relive those horrible moments in time, causing additional trauma. We do not know how many victims of the theater shooting would like to see our son killed. But we are aware of people's sentiments. We have read postings on the Internet that have likened him to a monster. He is not a monster. He is a human being gripped by a severe mental illness." 

Holmes' lawyers said in court that although the defendant was the lone shooter he was undergoing a psychotic episode, USA Today reported. 

Prosecutors said that although Holmes may have been disturbed he appeared to know what he was doing because the evidence shows he planned out the attack.