As a detective interviewed him, he started pretending the paper bags on his hands -- meant to preserve gunshot residue -- were puppets.
The former neuroscience student tried to jam a staple into an electrical outlet. He played with a cup on the table. An officer noted that his eyes were dilated.
The description came as prosecutors tried to show that Holmes should face a trial for the July 20 attack at a midnight showing of The Dark Knight Rises. He faces more than 160 felony charges for allegedly killing 12 and injuring 70.
Defence attorneys say Holmes is mentally ill. They said they might call witnesses later this week who could discuss Holmes' mental health.
The description of Holmes after the attack, given by police detective Craig Appel, seemed to undercut prosecutors' attempts to show Holmes as methodical, spending two months to assemble his arsenal.
He first bought two tear gas grenades, ordered online May 10. Holmes also bought two Glock handguns, a shotgun and an AR-15 rifle, along with 6,295 rounds of ammunition, targets, body armour and chemicals, prosecutors said.
He dyed his hair orange, bought a scope and non-firing dummy bullets on July 1. Finally, he purchased glycerin and potassium permanganate -- chemicals that could combine to create fire and sparks -- from a Denver science store. He improvised napalm, as well as thermite, a substance which burns so hot that water can't extinguish it.
Holmes' purchases were split between two planned attacks, prosecutors said -- the theatre shooting and a booby-trapped apartment.
The bottle of glycerin was meant to fall into the permanganate when the door opened, to cause an explosion and then a fire, prosecutors said.
Parts of Holmes' carpet were soaked with gasoline and oil and ammonium chloride, a white powder, was poured onto the floor in strips, FBI bomb technician Garrett Gumbinner said. "It would have ignited and the apartment would have exploded," he said.
He said the system had other initiating systems. One was a pyrotechnics firing box that would have been triggered by the remote control unit of a toy car left along with a system to play loud music. Gumbinner said Holmes told him he hoped the music would lure someone and lead them to play with the car, thereby detonating the explosives.
Holmes, dressed in body armour, was found outside the cinema. He told police the booby trapped apartment was an effort to pull police away from the cinema so, under that scenario, he wouldn't expect to see police so quickly.
Prosecutors also used his dating website profiles to try to prove he knew what he was doing. On Match.com and FriendFinder.com, Holmes asked: "Will you visit me in prison?"
If Holmes is found sane and goes to trial and is convicted, his attorneys can try to stave off a possible death penalty by arguing he is mentally ill.
If he's found not guilty by reason of insanity, he would likely be sent to the state mental hospital, not prison.