Investigators are narrowing down the possible cause of the collision between two Amtrak trains in Connecticut on Friday. They are considering the possibility that the crash, which resulted in the injuries of more than 70 people, was caused by a fractured segment of track they discovered on the rail line of a Metro-North passenger train. Three people are still in critical condition.

The fractured rail could have caused the derailment of the eastbound train, which led to the crash when it left the track and collided with a train coming in the opposite direction bound for New York’s Grand Central Station.

Foul play has been ruled out in Friday’s collision by the investigators. The two Amtrak trains collided during the evening rush hour between the towns of Bridgeport and Fairfield.

Further investigation is needed before all other potential causes can be ruled out, but that stretch of rail line has undergone repair work during the past month, according to Metro-North officials.

According to Earl Weener, a board member for the U.S. National Transportation Safety Board:

“We do know that the back end of the eastbound train that derailed went over that part of the track where there is a fracture, and that there was repair work done on that stretch of track within the past 30 days.”

The segment of the train track believed to be responsible for the accident is undergoing tests that might prove that it was the cause of the accident.

“There were people on stretchers. There were people lying on the ground,” said passenger Frank Bilotti, returning from a business trip in Boston on the westbound train when it crashed.

“All of the injured people described the really harrowing experience of having the train jolt to a stop, the dust, darkness, other kinds of factors that made it particularly frightening,” said U.S. Sen. Richard Blumenthal, who visited several patients in the hospital mere hours after the accident occurred.

The New York-New Haven line is the busiest rail line in America and serves 125,000 commuters a day, according to Judd Everhart of the Connecticut Department of Transportation.

U.S. Sen. Chris Murphy said it was “frankly amazing” people weren’t killed in the crash.

Among other evidence, NTSB investigators will look at the brakes and performance of the trains, crew performance and train signal information.

After the investigation is concluded, Metro-North will begin the process of removing the damaged rail cars and remaining debris. Once that is done, Metro-North can begin the work of rebuilding the damaged tracks and overhead wires.

Already, the NTSB investigators have allowed Metro-North to begin removing some of the track and wire from the scene.

Bridgeport Mayor Bill Finch said the Amtrak two-train collision and the disruption caused by the crash could end up costing the region’s economy millions of dollars.

Amtrak, as a result of the Metro-North derailment and two-train collision, has indefinitely shut down service between New York and Boston.

Written by: Douglas Cobb