Assistant Chief Constable Steve Cotterill said "please do not see these two arrests as the police inquiry coming to an end" and appealed to the public for additional information.
He said: "I need additional information from the public out there to really get to the truth to what was the reason behind that fire - whilst I know the cause I do not know the reason behind it and I'm still anxious for that information to come forward."
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Another unsettled day with cloud, rain and blustery winds.
Charaf Elmoudden, 26, has been found guilty at Harrow Crown Court of burgling pop star Rita Ora's home.
Buried here are the men of the 10th West Yorks, the unit that suffered the heaviest losses on the first day of the Somme.