According to fire investigators, a transient who was squatting at the house woke up to find his mattress on fire, and tried to put it out.
That's when he suffered the burn injuries.
Meanwhile, the mattress somehow wound up on the deck, lighting it on fire, before igniting part of the house.
It is unclear whether the transient was sleeping outside, or if he moved the mattress.
There is no word yet on a cause.