A secret CIA museum that had been closed to the public recently allowed NBC to bring video cameras in.

The museum, known as the "coolest museum you'll never see," has a new addition to their collection, the gun found next to the body of Osama bin Laden during the raid in Pakistan by Navy SEALs.

The weapon is an AK-47 and it's in a museum that is tucked into the hallways at the CIA headquarters in Langley, Virginia. The museum displays gadgets, artifacts and trophies resulting from 70 years of spycraft. It dates back from Wrld War ii through to the War on Terror.

Bin Laden's weapon, which is Russian-made, is stored next to an al Qaeda training manual that was found in Afghanistan.

"this is the rifle that was recovered from the third floor of the Abbottabad compound by the assault team," Toni Hiley, the museum's curator. "Because of its proximity to [bin Laden] there on the third floor in the compound, our analyst determined it to be his.

"It's a Russian AK with counterfeit Chinese markings," Hiley continued.

The agency won't say how the weapon ended up in the museum, but according to one source who spoke to NBC, it came from the "dark side" of the agency, the operations staff that worked with the SEALs on the May 2011 raid.

"I wasn't there," Hiley said. "So I can't confirm or deny exactly where the weapon was.

"I just know that I have it in my museum and I'm happy to have it," Hiley continued.

The movie "Zero Dark Thirty" showed a member of the Navy SEAL assault team grabbing the weapon after bin Laden was killed. The movie was written in consultation with military and intelligence sources.

The weapon is in good condition, according to Hiley. However, the origin of the Chinese markings are a mystery, and it's not the same weapon seen with bin Laden in his many propaganda videos.

The private museum was started in the early 1990s and fills three corridors in two buildings at the CIA headquarters outside Washington.

The museum follows the CIA's history from its origin as the Office of Special Services during World War II through the Cold War and Vietnam, and even has the movie script and briefcase used in the mission to rescue Americans from Iran in 1979, made famous last year in the film "Argo."

Some pieces from the museums collection are viewable online on the agency's web site.

There is also another secret museum behind this secret museum, where a "classified collection" is kept in a secret warehouse.

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NBC coverage of the CIA museum.