At least 12 people were killed and dozens were injured in a shooting during an early morning screening of the new Batman movie at a Colorado theater.
One of the injured is believed to be as young as 3 months old, hospital workers say.
Police arrested a man believed to be the shooter in a rear parking lot of the theater in Aurora, a suburb of Denver.
Two federal officials confirmed the suspect as Colorado resident James Holmes, 24.
Police said there was no evidence of a second gunman, and it doesn't appear the incident was related to terrorism.
Chaos broke out during the showing of "The Dark Knight Rises" at the Century Aurora 16 theater when the shooting began.
Police said the gunman "appeared" in the front of the theater and threw a smoke bomb before opening fire. Sources say the smoke bomb was tear gas.
Cell phone video taken by someone at the theater showed scores of people screaming and fleeing the building. Some had blood on their clothes.
One police officer carried a girl believed to be about 9 with gunshot wounds to her back out of the theater, a witness said. "She wasn't moving."
Police are now searching an apartment building at 17th and Paris streets where Holmes apparently lived.
Here the bomb squad prepares to check Holmes' vehicle.
The shooter used at least four guns -- an "AK type" rifle, a shotgun and two handguns, the federal law enforcement official told CNN.
Law-enforcement officers who searched the the suspect's apartment found "items of interest," a federal law enforcement source involved in the investigation told HLN.
In addition to looking into the possibility of explosives, ATF agents also are conducting emergency traces on the weapons used to see how they were obtained.
Aurora is about 13 miles from Littleton, Colo. -- site of the April 1999 Columbine High School massacre.