"We believe we have eliminated the major threats there, but we still have some more work to do," Aurora Police Chief Dan Oates said.
Oates said James Holmes' apartment undoubtedly was "designed to kill whoever entered it," USA Today reported.
"If you think we are angry, we sure as hell are angry," the police chief said. "There is no question about what the intent was of whoever designed that device behind that door."
FBI Special Agent John Yacone said the effort to disarm the explosive devices "went very, very well, but the threat has not been completely eliminated. It has been significantly reduced."
The Los Angeles Times reported the controlled detonation was set off inside the Aurora apartment after several blocks of nearby Peoria Street were evacuated. One of the bomb squad members working to disable explosives inside the apartment cried "fire in the hole!"
A bomb expert said about 30 softball-sized explosive devices were strewn around the 800-square-foot apartment's living room, The Denver Post reported.
Technicians sent in a robot with an explosive device. The Post said the device was dropped and the robot withdrew.
When technicians triggered their device they heard only one explosion, and they believe a trip device was destroyed, the Post said. Afterward, technicians were to decide whether officers may enter or whether the robot needs to be sent in again.
Yacone, at a news conference with city and state officials, said residents probably could return to the area by Sunday. Oates said the suspect had a high volume of deliveries to his apartment during the last four months.
"If a neighbor ... would have walked through that door, they would have sustained significant injuries or they would have lost their life," Yacone said.
Oates said FBI profilers would be trying to determine what the suspect's motive was for the killings.
Aurora police Sgt. Cassidde Carlson said the "best of the best" were deployed to examine the apartment and dismantle or detonate the booby traps, USA Today said. Residents of the building and four others nearby were evacuated and several small businesses forced to close.
Holmes, 24, a graduate student in neuroscience at the University of Colorado, was arrested at a movie theater where he allegedly opened fire early Friday during a midnight showing of "The Dark Knight Rises." Twelve people were killed and scores wounded. He is to have an initial court appearance Monday.
Several hundred people gathered at a vigil Friday night near the theater. The vigil had been planned for weeks for victims of violence but pastors decided to move it across from the theater after the shootings there, the Post said.
Mourners held candles, hugged, prayed and sang songs in the parking lot until after sundown.
"Since this happened, we said it is time to come together," said Thomas Mayes, pastor at the Living Water Christian Center Church in northwest Aurora.
"The brazenness of this violence seems to keep rising," said Patrick Demmer, pastor at Graham Memorial Church of God and Christ.
Brian Rohrbough, the father of Daniel Rohrbough, who was killed in the Columbine High School shootings in Colorado in 1999, urged mourners to reach out to families and friends of the victims of Friday's shootings.
"I encourage you to recognize God didn't put us here on the Earth to be on the sidelines," Rohrbough said. "Tell them you are praying for them
Shortly after prayers ended, a group of teens learned that a high school classmate had died. Girls sobbed and several boys hugged.
A prayer vigil was planned for 6:30 p.m. Sunday in Aurora.
Holmes allegedly told police he had rigged the apartment with explosive.
"I see an awful lot of wire, trip wires, jars full of ammunition, jars full of liquid and ... things that look like mortar rounds," Oates said.
A shelter was set up at Aurora Central High School for those forced from their apartments.