A congressman has confirmed a "stand down" order was given to a rescue team that could have responded almost immediately to the shooter running amok at the Washington Navy Yard more than a week ago.

In an interview with Jake Tapper of CNN, Rep. Michael McCaul, R-Texas, said his information came from a member of the rescue team.

Ultimately, authorities said, 34-year-old Aaron Alexis was shot and killed by police after he allegedly shot two dozen people at his place of work, killing 12.

The Atlantic Wire and other outlets reported several days after the attack that there was a "tactical unit of heavily armed Capitol police" near the scene "as it happened, ready and capable of stepping in."

But multiple sources, according to the report, said the unit was ordered to stand down.

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The Wire report said the officers were part of a four-person Containment and Emergency Response Team with routine responsibilities of guarding the Capitol. But they were wearing full tactical gear and armed with assault weapons, the report said.

They arrived on the scene of an active shooting but were told, according to initial reports by BBC News, "to leave the scene."

Capitol police officials said they were investigating.

McCaul, in his interview with Tapper, said that agencies, reportedly, were having problems communicating with each other.

"The idea that we're not interoperable is really inexcusable, so we will be investigating that," he said. "I plan to hold a hearing on the House Homeland Security Committee on this issue."

He then referenced the "stand down" order.

"I just happened to bump into one of these SWAT team members outside the classified briefing room at the Capitol and he told me about how the … and I heard this firsthand, that his commanding SWAT team officer told them to stand down."

McCaul said team members were eating breakfast when the commanding officer told them to stand down.

"That's obviously of great concern when you have a SWAT team that close by that could respond to the situation," the congressman said.

"I need to verify the veracity of that statement. I've no reason to believe he was simply making this up, and so that's something obviously we're going to be looking into."

Earlier, Terry Gainer, the Senate sergeant-at-arms, described it as a very "serious allegation" to suggest the police were on the scene and could have helped but were sent away.

A police department official in Washington told the BBC it might have been a misunderstanding.

It's the second time recently in which an alleged "stand down" order has made headlines. Critics of the U.S. government's handling of the terror attack on U.S. diplomats in Benghazi, Libya, a year ago charge a team was preparing to assist but was told to stand down.

Four Americans died there.

McCaul's interview: