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
Cloudy at first with outbreaks of rain, sleet and hill snow possible.
Remaining cold with bright spells and further scattered rain and sleet showers, with snow becoming increasingly restricted to hills.
Cold, with some wintry showers at first, but with any snow becoming confined to the hills.