An act of sabotage by someone with railway know-how could be to blame for the crash at Potters Bar near London, according to the firm in charge of maintenance on the line.
Jarvis has put forward the theory that someone with knowledge of the mechanics of the track may have deliberately vandalised the set of points.
After the accident two sets of nuts were discovered lying on the ground by the track and a switch rail that shifts the train on to a different piece of track is thought to have been moved.
The damage caused the 12.45 p.m. King's Cross to King's Lynn service, on May 10th to derail at 100 mph, propelling the fourth carriage sideways on to Potters Bar station platform. Seven people died and 76 were injured in the crash.
Britain's Health and Safety Executive's (HSE) interim report into the accident, released earlier this week, stated that initial investigations showed that nuts may not have been replaced properly or that maintenance work had been left unfinished.
The HSE said that if vandalism had been to blame it would have had to have been of "an extremely sophisticated and daring nature".
But a spokesman for Jarvis said: "There's possible evidence of sabotage and it should be investigated fully.
"In terms of causing disruption to the railway, not necessarily to cause a major accident, it looks to us as if, if there was a situation of an outside person playing around with the points, it would be somebody who knew at least roughly what they were doing."
He said the company was not suggesting that a disgruntled former employee was responsible and said Jarvis was not trying to wriggle out of taking any blame itself.
"We don't know what caused the accident. We have come up with a number of factors that suggest to us external sabotage, not casual vandalism, and it should be looked at fully," he said.
PA