AURORA, Colo. -- Police in Colorado continue to investigate an early-morning shooting at a movie theater outside of Denver, Colorado.

Twelve people were killed and more than 50 others injured when a gunman walked into the theater during a showing of "The Dark Knight Rises."

Police said the shooter released a canister of gas and then began shooting randomly. He's been identified as James Holmes, a 24-year-old student at the University of Colorado. Police arrested him within minutes outside the theater.

Officials said when they arrived at his apartment, they found it booby trapped with bombs. They're now working to disarm them, before moving in to search.

Investigators said it appears Holmes acted alone.