Experts were sifting through the wreckage yesterday of a Washington DC train crash that killed at least nine people to discover what went wrong with computerised systems supposed to make such accidents impossible.

The collision of two trains during the Monday evening rush hour on the northeast border between Washington and Maryland was the deadliest incident in the 33-year history of the Metrorail service.

The trains had been heading towards downtown Washington at about 5pm. One had stopped on the track waiting to arrive at Fort Totten station when a second train smashed into the back of it.

Several of the dead were crushed and their bodies were not found until a crane removed sections of the train yesterday morning. At least 76 people were injured, including two who are in a critical condition. The impact of the crash was so powerful that the striking train was compressed to about one third of its original size, Adrian Fenty, the Mayor of Washington, said.

John Catoe, the general manager of the Washington Metropolitan Area Transit Authority, confirmed that the death toll had risen from seven to at least nine. “The scene is one that no one should ever see. There is unbelievable destruction and damage,” he said, adding: “What I saw was far worse than anything you can imagine.”

The only previous fatal accident on this fast and clean subway railway system was in January 1982 when three people died in a derailment.

Metrorail was designed with a signal system that uses on-board computers to control speed and apply brakes automatically to maintain a safe distance between trains.

Debbie Hersman, of the National Transportation Safety Board (NTSB), said: “We need to see if that system was actually what was being used at the time and if there were any faults. We’re going to be looking at the tracks, at the signal system and at the train operation to understand what happened.”

She said that the priority would be to find any event recorders that may have been on the trains. The NTSB had recommended previously that older cars be upgraded with better data recorders and Ms Hersman said that the agency found it unacceptable that Metrorail had not done so.

The older trains, which include the one that ploughed into the stationary carriages, make up about 30 per cent of the fleet and are being phased out.

Mr Catoe did not yet have a response about why the recommendations of the safety board were not followed.

The FBI is assisting NTSB teams with collecting evidence and dogs have been used in the search for victims. Takoma and Brookland stations, which neighbour Fort Totten, were closed during the investigation.

Tom Baker, 47, a passenger in the second train, described the moment of impact to The Washington Post. “You could hear all this crashing and glass breaking,” he said. “I didn’t hear any brakes at all.” He saw the train lift into the air, adding that “when the dust settled the entire front of the train was gone”.

President Obama sent his condolences. “Michelle and I were saddened by the terrible accident,” he said. “Our thoughts and prayers go out to the families and friends affected by this tragedy.”

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