WASHINGTON — (CNN) U.S. Capitol Police arrested a Senate employee at 7 a.m. Tuesday who had a loaded 9mm gun in a backpack as he went through security at the Dirksen Senate Office Building.

The gun was detected by an x-ray machine as part of normal security screening for people entering buildings on the congressional campus, according to Capitol Police Captain Kimberly Schneider.

Christopher Carpenter of Stafford, Virginia, was charged with unlawful activities and possession of unregistered firearms and ammunition.

Carpenter is the manager of the Senate ID office, which processes ID badges for people who work on the Hill, according to an official familiar with the situation. He will be on annual leave while law enforcement completes processing the charges and will then return to work, the official said.

Carpenter works for the Senate Sergeant of Arms, who oversees security in the Senate and handles other administrative duties.

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