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
The incident caused the Hagley Road to be closed. It's thought there are no injuries.
Two children reported seeing a boy approached by a man wearing all black and a mask, but the boy ran away.
Rain on the way, which could be heavy at times.