AURORA, Colo. — Police hope to enter the Colorado shooting suspect’s apartment today but have been forced to move cautiously after spotting booby traps with trip wires.

Firefighters are monitoring the Aurora apartment building for gases to determine what chemicals 24-year-old James Holmes might have used to trap the place in case the materials go off, authorities said.

Police evacuated the building and surrounding residences after arresting Holmes as the suspect in a mass shooting Friday at a midnight screening of “The Dark Knight Rises.” Twelve people were killed in the attack and about five dozen were injured, including 11 victims who remained in critical condition, authorities said.

FBI agents and police discovered it was booby-trapped when they used a camera at the end of a 12-foot pole to look inside.

“It’s a pretty extensive booby trap. We’re not sure what it’s attached to. There are trip wires. There are three containers and we don’t know what’s inside,” said Chris Henderson, deputy Aurora fire chief.

Police Chief Dan Oates said officers will try to enter today.