A U.S. Capitol police officer reportedly is under review Thursday after somehow leaving his Glock 22 pistol inside the bathroom of the structure's visitor center earlier this week.

Lt. Mike Byrd forgot to take the weapon with him upon leaving the restroom Monday and it was found “during a routine security sweep” later in the day, officials told Roll Call.

“The Department takes these matters very seriously, and has a very thorough process to investigate and review incidents such as these, and holds personnel accountable for their actions,” Capitol Police spokeswoman Eva Malecki said. “Following the investigation’s conclusion, appropriate actions will be taken in accordance with the Department’s official policies and procedures.”

Byrd is the leader of the House Chambers section of the department and was reportedly back on the job in the days after the incident. He allegedly told his colleagues he “will be treated differently” because of his rank, sources told Roll Call, although it wasn't immediately clear what he may have meant by the comment.

But it’s not the first time security personnel have left weapons behind on Capitol Hill.

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In 2015, an officer tasked with protecting Senate Majority Leader Mitch McConnell left his Glock and its magazine inside a toilet seat cover holder in the same visitor center.

Another officer, this time with former House Speaker John Boehner’s security detail, also in 2015, forgot a loaded firearm inside the Congressman’s office bathroom. The weapon was later discovered by a young child visiting with his family.