Canadian police said it was unclear if the inquiry into the Quebec train crash will lead to criminal charges and added that no arrests had been made so far.
The death toll from the Quebec train blast has risen to 15, Canadian police told Reuters.
The Queen has sent a message of support to the people of Canada following an oil train derailment and blaze that killed at least 13 people and wiped out the centre of a small town in Quebec.
Authorities are searching for remains in the wreckage of the crash almost three days after the disaster in the town of Lac-Megantic.
A total of 50 people are still missing, including the 13 unidentified victims, and the death toll is expected to rise.
The Queen said in her message: "It was with profound sadness that I learned of the tragic events that have befallen the town of Lac-Megantic.
"The loss of life and livelihoods has shocked us all. Prince Philip joins me in hoping that in time it will be possible to rebuild both the property and the lives of those who have been affected. My thoughts and prayers are with you all".
Inspectors examined the train involved in last weekend's rail disaster in Quebec the day before the fatal derailment, and found no problems with it. Canadian transport minister Denis Lebel said:
Canadian police say 13 people have now been killed in the Quebec runaway train blast.
About 40 people remain missing a day after a runaway train derailed in Quebec, igniting several fires that destroyed a city centre and killed five people.
Officials are warning the death toll will rise and there are fears further explosions may occur as two carriages filled with petrol have not ignited, as yet.
Only a small part of the devastated areas have been searched as fire fighters are focusing on ensuring the fires are out.
A coroner's spokeswoman said it may not be possible to recover some of the bodies because of the intensity of the blasts.
Canadian Prime Minister Stephen Harper has visited the scene of the train crash that killed at least five people in the town of Lac-Mégantic, Quebec, and said the area "looked like war zone. "
He said the incident was a "disaster in human terms and warned there were "many many people" still missing.
The operator of a train that rolled downhill and careened into a Quebec town, causing a deadly explosion, said the air brakes used to hold the locomotive in place may have been released after the train was parked.
The train had been hauling crude oil from North Dakota to eastern Canada, and was sitting parked, without a driver, outside town when it began to roll downhill, gathered speed and derailed on a curve at 1 am (0500 GMT) on Saturday.
The statement from Montreal, Maine & Atlantic Railway did not make clear how the brakes had been disengaged, or who could be responsible.
Canadian police have said the death toll from Saturday's rail blast disaster has risen to five and around 40 people are still missing, Reuters reports.