Washington police have ordered a review into a BBC report that an armed police team was ordered not to respond to the navy yard mass shooting.
A tactical response team from the force was told by a supervisor to leave the scene instead of aiding municipal officers, according to police sources.
The Capitol Police sources suggest they could have saved lives had they been allowed to go in.
Aaron Alexis, who was 34, killed 12 people at the Washington Navy Yard on Monday local time.
In a statement, the US Capitol Police Board said the force's Chief Kim Dine had asked it to conduct "a comprehensive, independent review of the facts surrounding the Capitol Police's response to the Navy Yard shootings".
