CENTENNIAL — For a few hair-tingling seconds, the downstairs neighbor of the Aurora theater gunman stood outside his door the night of the shooting — mere inches away from unintentionally triggering what police testified Wednesday would have been a terrible explosion.

During a court hearing focusing on the search of James Holmes’ apartment, Aurora police Sgt. Michael Holm testified that the neighbor went to the apartment door after loud music started playing in the apartment after midnight on July 20, 2012. The neighbor found the door ajar and decided to go back downstairs to call in a noise complaint to police.

Had she opened the door and walked in, she could have triggered the trip wire police later found behind the door, starting what investigators testified would have been a chain reaction setting off the multiple explosive devices in the apartment.

“If these would have gone off in that small of an area,” said Denver police bomb squad member Paul Capolungo, who responded to the apartment after the shootings, “it would have been devastating.”

It was that danger that investigators said Wednesday caused them to use a bomb robot to enter the apartment early July 20 — after statements Holmes made at the scene about bombs in his home. Capolungo was also later hoisted up in a fire truck’s bucket to break out windows to the apartment and peer inside. All that happened before police obtained a search warrant for the apartment later in the morning on July 20.

Defense attorneys argue those warrantless intrusions were improper and mean all evidence from the apartment should be thrown out at trial. Prosecutors say there are exemptions to the warrant requirement during emergencies.

“The exigency the police faced in entering the apartment was clear as glass,” prosecutor Rich Orman said Wednesday.

Arapahoe County District Court Judge Carlos Samour will issue a written ruling at a later date.

If he does toss the evidence, jurors will not be able to hear about the litany of things investigators testified Wednesday they found inside.

Aurora detective Thomas Wilson testified that police seized a notebook that contained a drawing of “some kind of maze game involving a serial killer and a downtown Denver address called LoDo’s” — it was not entirely clear whether Wilson was referring to the downtown bar by that name or the general downtown district.

The notebook was found in a backpack on the floor of the living room, and the backpack also held a withdrawal form from the University of Colorado Anschutz Medical Campus, Wilson said. The form had not been signed by Holmes.

Wilson said police also took prescription bottles — including one for a drug called sertraline, more commonly known as Zoloft — as well as cable gun locks, a petri dish, a shooting target stand and a note from Holmes’ mother about insurance. FBI special agent Leslie Kopper testified that investigators also found a Batman costume mask, a receipt for a movie ticket and a plastic bag with metal clips similar to the one used to hold open the exit door to the theater where the shooting occurred.

Kopper said investigators also seized a calendar that was unusual because it had only one day marked on it: July 20.

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