Fatal Philadelphia fire investigation getting help from national response team

A National Response Team is being activated to help with the investigation into Wednesday's devastating fire in Philadelphia.

A residential fire in a converted apartment building killed 12 people, including eight children. Officials initially reported 13 people had been killed while conducting search and recovery efforts.

When firefighters arrived, they found heavy smoke, heat and limited visibility on all floors.

The Philadelphia Fire Marshal's Office is leading the investigation into the cause of the fire along with help from the Philadelphia Police Department and the federal NRT, part of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The deployment of the NRT came at the request of the Philadelphia Fire Marshal's Office given the magnitude and the scope of the fire, the bureau said in a statement.

"We're grateful for the assistance as we continue to investigate the heartbreaking fire on 23rd Street," the Philadelphia Fire Department said in a tweet.

Firefighters were able to rescue one child from the fire, but the child didn't survive.

"This is a very tragic event in which the community sustained such a great loss of life," said Matthew Varisco, special agent in charge of ATF's Philadelphia Field Division. "ATF will continue to work with our local, state, and federal partners to assist in any way possible."