Police said he volunteered information about the booby traps. Authorities went to the apartment and carefully dismantled them.
Prosecutors also used Holmes' dating website profiles to try to prove he knew the consequences of his planned actions. On two social networking websites — Match.com and FriendFinder.com — Holmes asked: "Will you visit me in prison?"
The Match profile was created in April; the FriendFinder account was opened on July 5. Holmes last accessed the sites two days before the shooting, detective Tom Welton testified.
Defense attorney Daniel King asked Appel if Holmes was tested for drugs or other substances.
"I saw no indication that he was under the influence of anything," Appel said.
Holmes' lawyers could have waived the first public airing of the case against him, but legal analysts say they may see the mini-trial as a chance to gauge the prosecution's case or tactics to prepare for a possible plea agreement.
Cases rarely advance to this stage without a judge agreeing to set a trial.
If Holmes is found sane, goes to trial and is convicted, his attorneys can try to stave off a possible death penalty by arguing he is mentally ill. Prosecutors have yet to say whether they will seek the death penalty.
If he's found not guilty by reason of insanity, he would likely be sent to the state mental hospital, not prison. Such a defendant is deemed not guilty because he didn't know right from wrong and is therefore "absolved" of the crime, said former Jefferson County District Attorney Scott Storey.
Last year, Bruco Strong Eagle Eastwood was acquitted by reason of insanity of attempted first-degree murder in the wounding of two eighth-graders outside a school not far from Columbine High School. Eastwood is spending time in a mental hospital. His case will be reviewed every six months until he's deemed sane and released.
Associated Press writers Thomas Peipert, Nicholas Riccardi and Colleen Slevin contributed to this report.