Police in Colorado say the booby-trapped home of cinema shooting suspect James Holmes has now been cleared of explosives.
Specialist teams have been making the apartment safe.
Holmes is accused of opening fire at a screening of the latest Batman film in the Denver suburb of Aurora, killing 12 people and leaving dozens more wounded.
The devices left in the apartment could have killed first responders and destroyed the complex in a massive inferno, an official involved in the probe said on Saturday.
Bomb experts entered the 800-square-foot property after a controlled explosion.
Inside they found 30 aerial shells filled with gunpowder, two containers brimming with liquid accelerants and an unknown number of bullets left to explode in the resulting fire, according to a law enforcement official with expertise in improvised explosives.
“Make no mistake, this apartment was designed, I say, based on everything I’ve seen, to kill whoever entered it,” added Dan Oates, Aurora police chief.
“Who was most likely to enter that location after he planned and executed this horrific crime? It was going to be a police officer so, make no mistake about it, what was going on there,” he continued.
A coroner has released the identities of those who were killed during Friday’s shooting rampage. They are aged between 6 and 51.
US President Barack Obama will travel to Aurora on Sunday to visit the families of the victims.
“The federal government stands ready to do everything necessary to bring whoever’s responsible for this heinous crime to justice,” Obama said in a televised address.
“We will take every step possible to ensure the safety of all our people. And we will stand by our neighbours in Colorado during this extraordinarily difficult time.”
Suspect James Holmes is due to make his first court appearance on Monday.