A Bush Master AR-15 assault rifle similar to one used in Friday's rampage is displayed Sunday at a gun shop in Aurora, Colorado.The semi-automatic rifle used in the Colorado theater killings jammed during the rampage, apparently because of a problem with the 100-shot magazine feeding it, a law enforcement source with direct knowledge of the investigation said Sunday.
The military-style AR-15 had a separately purchased drum magazine, which can have trouble feeding bullets into the firing chamber if the gun is fired rapidly, the source told CNN.
"These after-market extended magazines have a tendency to jam," the source said.
Obama flies to Colorado