A fire that damaged a cancer research centre was caused by welding work, an investigation has concluded.
A report found hot debris from the roof of the Cancer Research UK Manchester Institute fell down a wall and set fire to cardboard and fabric on 26 April.
Helix Roofing said that was "unlikely" and has seen no clear evidence of it.
In its report, Greater Manchester Fire and Rescue Service also said people stole tools after the fire, as reported in the Manchester Evening News.
No-one was hurt in the blaze at the Christie hospital building which caused hundreds of thousands of pounds of damage.
Much of the research work was salvaged, Christie said.
Watch manager Michael Broadley, who was author of the report, concluded after extensive forensic investigation the fire at the Paterson building was due to welding operations being undertaken that day.
Helix Roofing Ltd said in a statement: "It appears someone has to be blamed even if there is no clear evidence.
"We do not believe that Helix caused the fire, our operatives are conscientious and well trained."
It added: "Our expert stated that the welding process was unlikely to have caused the fire after the reconstruction... and we have seen no clear evidence that persuades us [otherwise]."
The report also said that during investigation work unknown persons gained unauthorised entry to the roof and removed some power tools and hand tools.
This has never been explained or the people responsible identified, it added.
In a statement, Christie said the safety of patients and staff was "paramount" and it supports "any further work the fire service feels is appropriate with regards to fire safety" to ensure lessons can be learnt.
Research work was moved temporarily to the Alderley Park bioscience campus near Macclesfield, Cheshire in November while work on "ambitious plans" to redevelop the centre takes place.