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.
More top news
CCTV footage has been released of a "heartless" burglar who stole a man’s mobility scooter, leaving the 56-year-old housebound.
Police have launched an urgent appeal after a prisoner convicted for a violent robbery in Derby escaped from HMP Dovegate in Staffordshire.
A cool and breezy day with some bright or sunny spells and patchy cloud. A risk of a shower in the north into the afternoon.