Federal investigators are looking into the deadly crash of two Metro transit trains to see why the computerized system failed to work even though the emergency brake was pushed down.

What we are trying to understand is how the automatic train control system works and if there were any faults, said Debbie Hersman of the National Transportation Safety Board.

At the time of the crash, the train was operating in automatic mode, meaning it was controlled by computer. In that mode, the operator's main job is to open and close the doors and respond to emergencies, federal investigators said.

Officials say the emergency brake control was pushed down and there was evidence that the operator tried to slow her car before impact.

That train was never supposed to get closer than 1,200 feet period, said Jackie Jeter, president of a union that represents Metro workers.

Emergency brake controls are referred to as mushrooms on transit trains, protruding from the operator's console so they can be slammed down with a swift slap of the palm.

Debbie Hersman, an investigator with the National Transportation Safety Board, said Tuesday it wasn't clear when the button was pressed or how it got that way.

Now investigators are trying to test the automatic controls for Metro trains for the first time on Wednesday.

All Metro trains were running on manual control Tuesday as a precaution against computer malfunction.