Police: Trip wires, jars full of ammunition found in suspected gunman's apartment July 21, 2012 -- Updated 0327 GMT (1127 HKT) The suspected gunman booby-trapped his apartment, police say Attempts to enter the apartment are postponed until Saturday, police say Robots are sent in to get a better idea of what is inside, a source says (CNN) -- Authorities are postponing until Saturday any attempt to enter the booby-trapped apartment of a suspected gunman accused of opening fire in a crowded movie theater in Aurora, Colorado, the police chief said. Police evacuated five buildings Friday, including the one where shooting suspect James Holmes lived, after he told them he had rigged his one-bedroom apartment with explosives. It is a very vexing problem how to enter that apartment safely. I personally have never seen anything like what the pictures show us is in there," Police Chief Dan Oates told reporters Friday night. I see an awful lot of wire, trip wires, jars full of ammunition, jars full of liquid and ... things that look like mortar rounds. With the help of the federal government, Oates said the police department was bringing in "extra resources to consult on exactly how to deal with the problem." Holmes told police shortly after he was apprehended in the rear parking lot of the movie theater that he had rigged his apartment, according to Oates. Police arrived at Holmes' apartment to find "techno-music" blaring from the one-bedroom, according to a law enforcement source, who spoke on condition of anonymity. The music was on a timer and apparently started once he left for the movie theater, said the source, who was not authorized to release details of the investigation to the media. Robots were sent into the apartment Friday and investigators, including members of a bomb disposal unit, are going over the video and other information collected from inside, the source said. Oates said it could take days to work through the apartment safely. While authorities did not release an exact number of residents evacuated from the building, the number is estimated to be in the hundreds. By Friday night, authorities began allowing families in four of the five evacuated building to go back in to their residences one-by-one to retrieve personal items, such as medication, identification cards and clothing. A shelter was set up at Aurora Central High School for those forced from their apartments. CNN's Susan Candiotti and Chelsea J. Carter contributed to this report.