Batman Shooting.

CNN) -- A heavily armed gunman tossed tear gas into the darkness of an Aurora, Colorado movie theater Friday and then sprayed the audience with gunfire during an early morning screening of the new Batman movie, killing 12 and wounding 38 others, authorities said.

One of the injured was just 3 months old, according to hospital workers.

Police arrested a man believed to be the shooter in a rear parking lot of the theater, Frank Fania, a police spokesman, told CNN. The suspect was not immediately identified. Police said he was a man in his 20s from Aurora.

"He did not resist. He did not put up a fight," Fania said. Police seized a rifle and a handgun from the suspect, and another gun was found in the theater, he said.