An aide for Sen. Jim Webb (D-Va.) was arrested Monday morning for carrying a bag containing his boss’s loaded handgun and two additional magazines of ammunition into a Senate office building.

Phillip Thompson, a former Marine and longtime friend of Webb’s, was taken into custody by Capitol Police officers without incident at a door to the Russell Building after the pistol was discovered during a routine X-ray of his bag.

“It was determined that there was no intent to harm anyone,” Capitol Police spokeswoman Sgt. Kimberly Schneider said.

“To our knowledge, this incident was an oversight by the Senator’s aide,” Webb’s spokeswoman said in a statement released Monday afternoon. “Phillip Thompson is a … trusted employee of the Senator. We are still awaiting facts.”

Thompson, who was bringing the bag into the building after Webb returned to Washington, D.C., from an out-of-town event, now faces felony charges for carrying a pistol without a license. Webb left the gun with Thompson before leaving town last week.

“This doesn’t look at all like an attempt to smuggle a gun into the building,” said Senate Sergeant-at-Arms Terrance Gainer. “But the violation for which the person is charged doesn’t leave any ‘intent’ leeway. Our regulations up here are pretty clear about who can have a loaded firearm and where it can be and what it takes to bring an unloaded firearm onto the campus.”

Although the D.C. prohibition against firearms was put into place in 1975, under a provision in federal law Members of Congress and their staffs are in essence given the right to bear arms on Capitol grounds.

According to Capitol Police Board regulations established in 1967, Members and their aides are allowed to transport licensed firearms on the Capitol grounds in the course of carrying out their official duties provided the weapons are “unloaded and securely wrapped.” (Directives published in recent years also state that staff must be verified by Capitol Police.)

Although the regulations expressly prohibit weapons on the floor of either chamber, as well as in the adjacent lobbies, cloakrooms and galleries, individual Members are allowed to “maintain firearms within the confines of [their] office.”

But while Members and aides would technically have to violate District law just to transport a handgun to the Hill, Capitol Police are not under any obligation to report the offense to D.C. authorities.

Without naming Webb specifically, Gainer said Monday that he had been in contact with the Member’s office and that “they feel very bad for the individual. Apparently he did not understand the rules. They are concerned about this and they are trying to understand what the rules and regulations are and help out this individual who is at best an innocent offender in this thing.”

Monday’s case was certainly not the first time a staffer has been taken into custody for violating Capitol Hill’s firearm policy.

In April 1999, an aide to then-Rep. Bob Ney (R-Ohio) was arrested at an entrance to the Longworth House Office Building after a handgun, which he said he had forgotten was stashed in the laundry bag he was carrying, set off a metal detector. He was charged with a misdemeanor.

Gainer said that “there’s a lesson to be learned,” that Members, “especially new Members and their staff,” might not be familiar with Capitol Hill’s weapons laws.

“We’ll ensure that we get something out to refresh people’s memory about what the rules are,” he said.

In the meantime, Webb’s handgun remains in Capitol Police custody.

“In general, the owner of the confiscated property would have to come in in person and prove ownership or perhaps do that through their attorney” in order to get it back, Gainer said.