Security breach at US Capitol: Massachusetts man arrested outside library of Congress with gun

A man from Massachusetts was found carrying a firearm after visiting the US Capitol and departing the Library of Congress on Tuesday, according to police officials who spoke to ABC News on Thursday.

Police in Carlisle, Massachusetts, notified Washington authorities on Monday about an armed individual who had shared suicidal thoughts on social media and was travelling to Washington.

The individual was located in a Washington hotel early Tuesday by US Secret Service and Washington Metropolitan Police who interviewed him. Sources indicated that although they searched for a weapon, none was found, and no further action was taken at that time.

The man subsequently passed through a Capitol police magnetometer screening to enter the Capitol visitor centre. Despite the magnetometer triggering an alarm, "an officer performed a secondary hand search, and the man was let into the building," as stated by US Capitol Police.

Following his security clearance, Capitol police issued an alert about his presence. They found him outside the Library of Congress after he completed the full Congressional tour, discovering a 9mm handgun in his waistband, according to law enforcement sources.

The suspect faces charges including "Unlawful Activities, Carrying a Pistol Without a License, Possession of an Unregistered Firearm, Unlawful Possession of Ammunition, and Resisting Arrest." The US attorney's office is handling the case, per the Capitol police statement.

The officer responsible for the magnetometer screening at the Capitol Visitor Center "is suspended while the USCP's office of professional responsibility is conducting an administrative investigation into the officer's performance of that search."

Capitol police said there was no evidence suggesting intent to harm Congress. However, sources informed ABC News that a potentially suicidal individual managed to complete a full Congressional tour whilst armed, with both public visitors and Congress members present.

Capitol Police announced, "A full review of this incident has already been ordered, as well as mandatory refresher training on security screening, so this never happens again."

Congress members received a briefing about the incident on Thursday.