A large blaze at a derelict city centre building was started deliberately, a fire service believes.
The fire broke out at the former Grosvenor Hotel near Temple Meads on Victoria Street, Bristol, on 18 October.
There were no casualties but a neighbouring building was evacuated.
Some eye-witnesses reported seeing flames up to 18m (60ft) in the air at the height of the fire.
Avon Fire and Rescue Service crews from as far afield as Bath and Weston-super-Mare were called to deal with the blaze.
The building was due to be refurbished as part of the Temple Quarter project.
A spokesman for Bristol City Council previously said the authority "remained committed to its ambition to support the redevelopment of the area to create a world-class welcome to Bristol at Temple Quarter".
Responding to the news that the fire service had finished its investigation, the council said a cordon would remain in place until the building was confirmed as safe.
An Avon and Somerset Police spokesperson said: "An investigation is being carried out into a fire at the former Grosvenor Hotel premises in Victoria Street, Bristol, which is currently being treated as deliberate.
"We'd appeal to anyone who was in the area of the former hotel on the evening of 18 October, to contact us if they saw or heard any suspicious activity in the area or if they have any information on who was responsible.
"We've already taken some calls from members of the public and we'll be following up all information provided."
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