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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Dozens of African-American former agents will receive $24 million in settlement of a class-action lawsuit alleging racial discrimination.
The case was triggered by wheelchair user Doug Paulley who boarded a bus but could not get on because a pram was in the wheelchair space.
A dog which recovered from being stabbed by her owner for urinating on a bag of cannabis has had to be put to sleep.