The Colorado Mental Health Institute is asking for an extension to the amount of time it has to evaluate Aurora movie theater shooting suspect James Holmes.

Holmes has pleaded not guilty by reason of insanity, prompting the judge in the case to order that Holmes undergo a psychiatric evaluation at the institute, in Pueblo. The judge has set a deadline for the evaluation to be completed at the end of July.

But, in a letter sent to Judge Carlos Samour on Wednesday and made public Thursday, institute superintendent William May wrote that the psychiatrist doing the evaluation would like to have until Sept. 16 to complete the assessment. May wrote that the psychiatrist — whom he did not name — is “reviewing an extraordinary amount of documentation.”

“The evaluator has established a tentative plan for completion of the examination, which will likely require testing, interviews and/or assessments by a psychologist and neuropsychologist,” May wrote.

In response to the letter, Samour scheduled a hearing in the case for Tuesday morning so that prosecutors and defense attorneys can debate the request. In an earlier order related to May’s letter, Samour said the request could have an effect on motions hearings currently scheduled for August, as well as the trial date, which is now set for February.

Holmes is facing the death penalty if convicted of murder for the attack on the Century Aurora 16 movie theater, in which 12 people were killed and another 58 wounded by gunfire. The court-ordered evaluation is seen as a critical step for the case, as jury verdicts in insanity cases often follow the evaluations’ results. Holmes’ attorneys, though, have suggested they may withdraw his insanity plea after receiving the results of the evaluation.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/john_ingold