James Holmes used 3 different kinds of guns during his assault on a Colorado movie theater ... including a high power assault rifle.
The Aurora PD says Holmes was in possession of an AR-15, a Remington 870 shotgun and a 40 caliber glock handgun when he was arrested this morning.
Cops say they found another 40 caliber glock in the shooter's car, located right outside the movie theater.
An AR-15 is a semi-automatic weapon ... capable of firing off hundreds of rounds per minute.
Below is a video of someone demonstrating the firing power of the AR-15 -- a civilian version of the M-16 assault rifle.
The Killer's Arsenal
7/20/2012 12:05 PM PDT BY TMZ STAFF
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