“We suspect a criminal activity,” Anton Rüsch, prosecutor in charge of the investigation told the ATS news service on Monday of the blaze that broke out on Sunday night.
According to the initial investigation, separate fires were started in two different administrative offices of the library, located on the Place Chauderon.
Rüsch said a person or persons tried to force open the door of a safe in one of the offices.
File drawers were opened and their contents strewn around the floor.
“My office no longer exists,” Frederic Sardet, head of the library and archival services, told ATS.
“My table melted.”
Smoke billowed from the building and it took 16 fire fighters equipped with five vehicles to quell the flames after the fire was reported around 8pm.
Water used by the fire brigade did not damage any of the library’s books.
However, Sardet told 24heures newspaper that a fine coating of soot covered them.
“It will be ncessary to clean all of them,” he said.
“That should take a week.”
Computers were also covered in soot.
The library will remain closed for at least a week while the cleanup continues.