U.S. Capitol Police officials have launched a review of reports that tactical team members were ordered by their commanders to leave the scene after they responded to the mass shooting Monday at the Washington Navy Yard.

A Capitol Police officer, who spoke on the condition of anonymity because he was commenting on an internal matter, said he thinks officers could have made a quick entry into the building where a gunman opened fire, killing 12 people.

“We were definitely the closest tactical team in the city,” the officer said. “It was at the scene very early on, within a couple of minutes. They were ordered to disengage and turn back. For what reason, we don’t know.”

A Capitol Police spokesman said the department “offered and provided mutual support and assistance” at the Navy Yard. A statement said the Capitol Police Board will lead an independent review.

U.S. Capitol Police Chief Kim C. Dine said that “nothing is more important to me than for us to be where we’re needed to protect lives and property, where appropriate. We’re going to find out what happened. We need to find out what happened.”

Read eyewitness accounts from the Navy Yard shooting.

The allegation — first reported by the BBC and WUSA-9 — does not specify where the team was located and at what point during the incident it arrived. It was not clear whether the Capitol Police would have entered the building along with D.C. police and other responders or whether D.C. police had asked them to respond.

D.C. Police Chief Cathy L. Lanier has said that patrol officers were at the gate within two minutes of being dispatched and that two active-shooter teams were in the building within seven minutes.

In an interview, Dine said he contacted Lanier twice that morning to offer personnel.

Meanwhile, Anthony Meely, the chairman of the labor union for the Naval District Washington Police, said seven officers were on duty at the sprawling base Monday morning, down from what he said was 12 before budget cuts three years ago. He said that only the chief was on roving patrol duty.

Meely, a sergeant, said naval officers first went into the building and confronted the gunman in an exchange of gunfire in the lobby. He said a contract guard was fatally shot as the chief yelled for him to take out his gun. A spokesman for the based could not be reached for comment Wednesday evening.