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
19-year-old Kyle Parish was sentenced to five years in custody at Nottingham Crown Court today after admitting rape.
Lincolnshire County Council claim £150mi could be saved if the current system of one county council and seven district councils is changed.
A Leicester couple shot dead in the Tunisia massacre were weeks away from celebrating their 50th wedding anniversary, an inquest has heard.