and a big danger to the people beyond the shooter with a good aim, particularly if a soft [unarmored] spot like the head was hit, and around the shooter unless the aim was perfect. With a high penetration round, i.e. hard/fmj, serious danger of ricochets also exists.
One big question is how did the perp get in the theater dressed in body armor, wearing or carrying a gas mask, and an assault rifle? Walk through the lobby? Use a side or back entrance? Side and back entrances are normally fire exits and only open from the inside, and are usually alarmed.
There is far more to this story.