Detective Sergeant David Speight says whoever caused the fires may have flash burns on their body.
Michael and Angela Broderick, who are both deaf, had a narrow escape when an arsonist destroyed their home in Burbage in Leicestershire.
Police are appealing for the public to contact them if they have any information.
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Brighter skies will develop through thisafternoon, though perhaps with the odd shower at times.
It will be a largely cloudy start with a band of rain sinking south across the area from midday.
An MP has provoked anger over comments she made on her Facebook page about junior doctors 'holding the NHS to ransom'.