AURORA, Colo. (AP) — James Holmes is accused of carrying out one of the worst mass shootings in recent U.S. history, but police say there was nothing illegal about the guns and ammunition he allegedly used during a Colorado movie theater attack.

"All the weapons that he possessed, he possessed legally," Aurora Police Chief Dan Oates said. "And all the clips that he possessed, he possessed legally. And all the ammunition that he possessed, he possessed legally."

The four weapons recovered following the shootings that killed 12 and left nearly 60 people injured at a suburban Denver theater were purchased by the suspect from retail gun stores in Colorado in the last two months, authorities said Friday.

A federal law enforcement officer said Holmes bought one of the four guns — the first of two Glock pistols — on May 22 at Gander Mountain in Aurora, Colo. The official spoke on condition of anonymity because the probe into the shootings is ongoing.

Larry Whiteley, a Bass Pro Shops spokesman, said records show that its Denver store followed federal rules in selling a shotgun and a Glock pistol to Holmes.

"Background checks, as required by federal law, were properly conducted, and (Holmes) was approved," Whiteley said in a statement.

Gander Mountain, which sold an AR-15 assault rifle believed to be used in the shootings at a movie theater in Aurora, said the company was in compliance with state and federal laws and that it was "fully cooperating with this ongoing investigation."

A second federal law enforcement official said Holmes had a high-capacity ammunition magazine in the assault rifle. Oates said a 100-round drum magazine was recovered at the scene.

The type of ammunition magazine Holmes is accused of using was banned for new production under the old federal assault weapon ban, said Daniel Vice, senior attorney for the Brady Center to Prevent Gun Violence.

When the ban expired in 2004, gun manufacturers flooded the market with the type of high-capacity magazines Holmes used Friday, Vice said.

Oates did not specify the type of rifle but said that experts told him "with that drum magazine, he could have gotten off 50 to 60 rounds, even if it was semiautomatic, within one minute. And as far as we know, it was a pretty rapid pace of fire in that theater."

Oates said Holmes purchased ammunition over the Internet, including thousands of rounds and multiple magazines for the assault rifle.

Authorities have said that Holmes had on an all-black ensemble of protective gear at the time of the shooting. An online seller of tactical police gear told the St. Louis Dispatch (http://bit.ly/Pssg9H ) that it sold more than $300 of equipment, such as an assault vest, magazine pouches and a knife, to Holmes on July 2.

Chad Weinman, the CEO of Missouri-based TacticalGear.com, said Friday that Holmes had purchased two-day shipping for the items. He said the expedited timing for the items showed "some relevance as to what kind of mindset he was in." A message left after business hours Friday by The Associated Press was not immediately returned.

Holmes is also believed to have hurled two gas canisters into the theater before opening fire.

Holmes' gun purchases include:

— On May 28, six days after buying the first Glock, he purchased the shotgun from Bass Pro Shops in Denver.

— On June 7, Holmes bought the AR-15 assault rifle at a Gander Mountain store in Thornton, Colo.

— On July 6, Holmes returned to the Bass Pro Shops store in Denver and bought the other Glock pistol.

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Associated Press writers Alicia A. Caldwell, Pete Yost and Eileen Sullivan contributed to this report from Washington.