BRIDGEPORT, Conn. (REUTERS) - A fractured segment of track has been found on the rail line of a Metro-North passenger train from New York that derailed in Connecticut and struck another commuter train, injuring more than 70 people, investigators said on Saturday.
Authorities have ruled out foul play in Friday's collision, which occurred during the evening rush hour between the towns of Bridgeport and Fairfield, about 80 km northeast of New York City.
Further examination is necessary to determine if track damage found at the site of the accident was a cause or effect of the train wreck, but that stretch of rail line had undergone repair work during the past month, officials said.
"We don't yet know whether the fractured train track caused the accident, or was caused by it," Earl Weener, a board member for the US National Transportation Safety Board, told reporters at a news conference in Bridgeport.
"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," Mr Weener said.
The segment of fractured rail was being sent for analysis.
The accident involved two trains from the Metro-North commuter line that runs between New York City and parts of Connecticut. The wreck occurred when several cars of an eastbound train headed from New York to New Haven, Connecticut, left the track and collided with a train coming in the opposite direction bound for New York's Grand Central Station.
More than 70 passengers and crew members were injured, officials said. Eight remained hospitalised on Saturday, three in critical condition, Connecticut Governor Dannel Malloy said.
The collision of the Metro-North trains forced Amtrak to shut down service indefinitely between New York and Boston.
The governor urged commuters who normally use the line to find alternative ways to get to work on Monday.
NTSB officials arrived at the scene on Saturday to begin their investigation, which has focused in part on recent construction and repair work in the vicinity.
"The FBI was involved at the beginning, but has determined, as have we, that there was no foul play involved," Mr Weener said.
"Frankly, we still don't know what caused the derailment and collision and will not have any answer to that question any time soon, certainly not while on site investigating," he said.
Mr Malloy said the train cars that derailed were new and "designed to the latest standards" for safety and protection of passengers.
"To the best of our knowledge, it is the first time that a car like this has been involved in this kind of incident, and by all appearances, they responded well," Mr Malloy said.
US Senator Richard Blumenthal of Connecticut told the news conference he had come directly from St. Vincent's Medical Center, where some of the passengers and crew were being treated.
He said he was particularly struck by the courage of one conductor hurt in the collision, a woman he identified only as Helen, who despite serious back injuries helped "many of the people off the train." "Considering the impact, we are very, very fortunate there were no deaths," Mr Blumenthal said.
Metro-North is operated by the Metropolitan Transportation Authority, a New York state agency.
The New York-New Haven line is the busiest rail line in America and serves 125,000 commuters a day, said Judd Everhart of the Connecticut Department of Transportation.