James Holmes is asking a judge to allow him to change his plea to not guilty by reason of insanity in the deadly Colorado theater shootings.

Holmes will seek the new plea at a hearing Monday. He faces murder and attempted murder charges in the July 20 attack, which killed 12 and injured 70.

No motive has emerged, but Holmes’ attorneys have repeatedly said their client is mentally ill.

Prosecutors are seeking the death penalty.

The insanity plea carries risks for both sides. Holmes must submit to a mental evaluation by state doctors, and their findings could be used against him by prosecutors.

The plea also makes it harder for prosecutors to get a conviction. They must convince jurors that Holmes was sane at the time of the shootings.