The head of the company that owns the train that exploded in a small Canadian town on Saturday says an engineer failed to set the brakes properly on the train.
Montreal, Maine Atlantic Railway chairman Edward Burkhardt faced angry residents when he arrived in Lac-Megantic on Wednesday to survey the devastation.
Mr Burkhardt previously blamed firefighters in another town for the disaster, saying they unwittingly unlocked the train's air brakes when they shut down the locomotive's engines to douse a small unrelated fire before the disaster.
Now, he says the shutdown of the air brakes was an important factor, but not the only one. But he added:
"The fact that when the air brakes released on the locomotive the train ran away would indicate that the hand brakes were not properly applied."
The confirmed number of dead after the disaster is 20 and 30 others remain unaccounted for following the disaster. Earlier, the number was reported to be 60.
The wreckage is being treated as a crime scene.
Quebec provincial police inspector Michel Forget said on Wednesday the confirmed death toll remains at 15, but 10 more people have been added to the list of missing or presumed dead in Lac-Megantic.
The blaze caused by the crash and explosion forced about 2000 residents to flee their homes on Saturday.
The train operated by Montreal, Maine Atlantic Railway had been stopped for a crew change in the nearby town of Nantes when it began to roll downhill without a conductor.
It derailed at a curve in the tracks and several cars exploded.