KNOXVILLE, Tenn. - It wasn't the preferred way to enter the Knoxville Museum of Art, but Richard Anthony Smith told police he was on a mission. The 25-year-old Knoxville man called 911 from his cell phone before dawn Wednesday saying he was trapped in an air conditioning duct leading from the museum roof, Knoxville police spokesman Darrell DeBusk said.

Police and firefighters reached the roof, found a rope and cable and followed them to a vent shaft. Peering inside, they spotted Smith about 45 feet down.

"Mission failed," he told them.

Hoisted up and read his rights, Smith told police he was a "special agent from the United States Illuminati, badge number 0931" and had rappelled onto the museum from a helicopter, a police report said.

He said he was following orders to "defuse and confiscate" a Soviet-made nuclear warhead, specifically a "MERV6SS-22AN" warhead, according to the report. The bomb supposedly was hidden in a blue, plastic cow sculpture in the museum basement, he said.

However, Smith told officers his "agency" called while he was in air-vent limbo to say it made a mistake and the bomb might be in a Memphis museum instead.

Police charged Smith with aggravated robbery. He was being held on $2,000 bond at the Knox County Jail. Authorities said he did not have a lawyer.

"Fortunately he was able to reach his cell phone," DeBusk said, "or he may not have been found for quite some time."