Authorities are investigating the death of a U.S. Marine who died of a gunshot wound early Tuesday inside a barracks on Capitol Hill in Washington, D.C., according to reports.

The gunshot was not self-inflicted, a D.C. police source told Washington’s FOX 5.

Authorities believe the Marine was killed by another Marine by accident, during a shift change around 5 a.m., when weapons are unloaded before being handed off to the next shift, the report said.

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The injured Marine later was pronounced dead at MedStar Washington Hospital Center, the Washington Post reported.

No arrests were made, and neither Marine was identified.

The deceased Marine was described only as having been in his early 20s, the Post reported.

Authorities stressed that the investigation was in its early stages, according to the newspaper.

The shooting was at least the third at the Capitol Hill barracks in the last six years, according to the Post.

The previous incidents were both self-inflicted gunshot wounds, with one of them being fatal, the newspaper reported.