A train driver who died in a crash near Bedford had passed a red signal moments before the collision, investigators say.
The Rail Accident Investigation Branch (RAIB) revealed the finding in a statement on Wednesday.
The driver, who died at the scene, has been named as 60-year-old Shaun Burton.
Mr Burton died when the East Midlands Railway (EMR) train he was driving hit the back of a stationary train run by the same operator.
The RAIB said in an interim report that Mr Burton's train proceeded past a red signal near the scene of the crash in Elstow, near Bedford, at 5.15pm on Friday.
It said that "it is not yet possible to say what indication the driver received" from automatic warning system (AWS) equipment fitted to the train.
Some 162 people were injured in the crash, with 102 needing hospital treatment.
Fifty-three remain in hospital, including eight in a critical condition.
Images from a CCTV camera on Mr Burton's train show a signal near the scene of the crash "was displaying a red aspect as the train approached and then passed it", the RAIB said.
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Preliminary analysis of a recovered data recorder shows the train was travelling at 76mph when its brakes were applied nine seconds before the crash.
Its speed had reduced to 49mph by the moment of impact.
The stationary train involved in the crash had come to a halt "unexpectedly" after a fault with its AWS equipment caused its brakes to apply, the RAIB statement said.
This resulted in the signal behind it automatically switching to red, investigators added.
Approaching trains must stop at red signals.
The RAIB said its full investigation will consider "the actions of those involved and any factors that may have influenced them".
It will also look at the "positioning, visibility and conspicuity" of the signal that Mr Burton passed.
Will Rogers, managing director of EMR, said it would be "inappropriate" to comment on "specific findings" or speculate on the circumstances of the crash "before all of the evidence has been examined".
While Dave Calfe, general secretary of train drivers' union ASLEF, asked why a train protection and warning system (TPWS) had not been installed where the crash happened.
The technology automatically applies a train's brakes when it detects it will be unable to stop before a red signal.
"If it had been installed, this accident would not have happened, the driver would not have died, and no passengers would have been injured," Mr Calfe said.
Transport secretary Heidi Alexander said her "deepest sympathies" are with everyone affected by the "tragic collision", particularly Mr Burton's family and those who are still in hospital.
She continued: "The report makes clear there is still much to establish, and the full investigation will provide the answers and recommendations everyone affected deserves.
"Our railway is one of the safest in the world, and while incidents like this are incredibly rare, when they do occur we will leave no stone unturned to understand what happened."
No timeline has been given for when the investigation will come to a close.
Meanwhile, British Transport Police (BTP) has asked passengers who left items on board the two trains to provide information about them.
BTP said it had "carried out extensive searches of the affected trains and recovered a significant amount of passenger property".
The items have been moved to an EMR storage facility and passengers are asked to get in touch with their contact information and details of which items they left.
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