BRIDGEPORT -- After a day of combing through the wreckage of two trains that collided during Friday evening's rush hour, federal investigators have found a broken rail, but they do not know if it was a factor in the eastbound train's derailment.

Federal investigators combed through Metro-North train wreckage Saturday in what promises to be a lengthy investigation into the cause of Friday night's rush-hour collision.

National Transportation Safety Board staffers pulled up in a caravan of cars along Commerce Avenue, joining an awaiting group of state and city officials for a mid-morning tour of the crash scene.

NTSB member Earl Weener told reporters the probe is focusing on the train's brake performance, condition of wheels, condition of tracks and signals.

"We'll also be looking at how the crew behaved (and) operated the train," Weener said.

He said data recorders should have been on board both trains, collecting their rate of speed and other information.

The goal is not only to determine what happened, he said, but seek to prevent it in the future.

The NTSB's working theory is that a Metro-North train heading east from New York City's Grand Central Terminal to New Haven derailed at about 6:10 p.m. just outside Bridgeport and was struck by a westbound train from New Haven to Grand Central on an adjacent track. About 700 were on board, 70 were taken to the hospital with two in critical condition.

The site of the wreckage is, essentially, being treated like a crime scene, with the media and curious onlookers kept at a distance while NTSB experts begin sifting through the debris for answers.

Weener said Day 1 is focused on time-sensitive, "perishable evidence."

That is going to be a daunting task, based on the descriptions from the elected officials who viewed the wreckage.

"The scene down there is enormously violent," said U.S. Rep. Jim Himes.

U.S. Sen. Richard Blumenthal said it looked like giant toys had been strewn throughout the area.

"The sides of cars are torn away like ribbons of cloth," Blumenthal said.

Weener added, "The tracks are very much torn up."

Asked about possible foul play, Weener said nothing could be ruled out at this stage.

With the Metro North line out of service between Bridgeport and Norwalk, Gov.