In 1990, a fire broke out in a house in Jacksonville, Fla., killing two women and four children. The husband of one of the women became the prime suspect, and that's when a fire investigator named John Lentini was called in.
At the time, Lentini says, the initial evidence pointed to a fire that was deliberately set. He calculated that it would have taken about 20 minutes for the house to become engulfed in flames — what's called a flashover — leaving plenty of time for someone to set the fire and get out.
