Police, ambulances and emergency crews swarmed on the scene after frantic calls started flooding the 911 switchboard, officials said. Officers came running in and telling people to leave the theater, Salina Jordan told the Denver Post. She said some police were carrying and dragging bodies.

Hayden Miller told KUSA-TV that he heard several shots. "Like little explosions going on and shortly after that we heard people screaming," he told the station. Hayden said at first he thought it was part of a louder movie next door. But then he saw "people hunched over leaving theater."

Officers later found the gunman near a car behind the theater. Oates said there was no evidence of any other attackers.

Holmes was a student at the University of Colorado School of Medicine in Denver until last month, spokeswoman Jacque Montgomery said. She did not know when he started school or why he withdrew.

At least 24 people were being treated at Denver area hospitals.

"Warner Bros. and the filmmakers are deeply saddened to learn about this shocking incident. We extend our sincere sympathies to the families and loved ones of the victims at this tragic time," the studio said.