Police: Colo. suspect bought guns legally, fired at least 100 rounds in theater

(CBS News) Law enforcement sources say Colorado shooting suspect James Holmes seems to be a classic lone wolf -- an accused mass killer with no apparent accomplices or known connections to radical groups. Prior to his arrest outside the Aurora movie theater where at least 12 people died early Friday, Holmes' only brush with Colorado police involved a single speeding ticket.

Holmes was completely under the radar. Yet, sources say, over the past few months he assembled a deadly arsenal: multiple guns, body armor, bottles of chemicals, and homemade explosive devices.

Colo. shooter purchased guns legally from 3 different stores

Sources say four weapons found at the crime scene were all legally purchased between May 22 and July 6 at three Colorado gun stores: a Bass Pro Shop in Denver and Gander Mountain stores in Aurora and Thornton.

Three of the guns were used in the deadly spree, police said. Both the .40 caliber Glock pistol and a Smith and Wesson semi-automatic assault rifle he used could be fitted with extended clips. A 12-gauge Remington shotgun was also used. A fourth gun, another .40 caliber Glock, was recovered in Holmes' car.

Evidence teams are still processing the crime scene. But with 71 victims hit by gunfire, law enforcement officials suspect the gunman fired at least 100 rounds.

Police say Holmes meticulously planned the assault. He apparently surveilled the theater and pre-staged his car and weapons near an access door. Outside that door police recovered some of the body armor, which the gunman wore during the assault.

Holmes has no criminal record and police have so far established no motive for the shootings. A search of social networking sites has turned up no significant clues.

Sources say Holmes was cooperative when first arrested, even warning police that his apartment was booby-trapped. But, so far he has offered no explanation whatsoever for the shootings.