![[ image: width=150]](/olmedia/65000/images/_68091_bus.jpg)
A source from the French Justice Department said traces of a flammable liquid were found at the site.
Though the fire was intentionally started, French law does not consider vandalism a criminal act, the source said.
Eurotunnel refused to comment on the verdict of arson.
A spokeswoman said: "We are not going to fuel any speculation, so we are unable to comment."
The fire broke out in an open freight wagon and caused the tunnel to close for months.
It left £200m of damage to be repaired and led eight truck drivers caught in the blaze to be taken to hospital.
According to French news agency sources, prosecutors in the northern French port of Bologne-sur-Mer have received the investigators' report concluding the fire was deliberate.
It is said to blame vandals for starting the fire, after a technical investigation last July ruled out a systems failure.
The findings have not officially been made public.
The spokeswoman for Eurotunnel added: "Once the judge has concluded the inquiry, we will speak but we have no firm date yet when that will happen."
![[ image: width=150]](/olmedia/65000/images/_68091_open.jpg)
The fire in the tunnel was a blow to the image of the much-criticised engineering feat.
The 30-mile path underneath the Channel linking Britain and France had only opened two years previously.
Although no one died, passengers suffered smoke inhalation and feared for their lives as they scrabbled to escape.
The flames took more than a day to fully put out and the knock-on effects lasted until June 1997 to completely repair.
Eurotunnel were criticised for their continued use of open wagons to transport large vehicles instead of covered carriers that would contain a fire.
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