GWEN IFILL: Finally tonight: a story of guilt or innocence. It's about a Texas man named Cameron Todd Willingham. A fire engulfed Willingham's home in 1991, killing his three daughters. Ultimately, a jury found him guilty of arson and of murder. He was executed in 2004.
Tonight's edition of "Frontline" examines the evidence. Here's an excerpt.
NARRATOR: Around town in Corsicana, Texas, Willingham's lack of serious injuries and a night of partying after the fire fueled rumors.
JOHN JACKSON, prosecutor: Immediately after the children were killed in the fire, he was seen at a local bar, essentially exhibiting behavior that was completely inconsistent with a person who had lost his three children.
VICKY PRATER, bar owner: When the Willingham children died, several of us thought it would be a good idea if we did a benefit dart tournament to raise funds to help with their burial. Todd and Stacy Willingham showed up the night that we had the tournament. Todd got too involved in the fun.
JOHN JACKSON: And he was heard to brag to others that he wouldn't have anything to worry about now, because the money would start rolling in, because people would feel sorry for him.
VICKY PRATER: He showed a great interest in a new pair of darts. That really kind of shocked me. I thought, well, you know, I'm really not going to let you give me back the money that I just gave you for a new pair of darts. So I just gave them to him, so that he wouldn't lose the money that I wanted him to spend on those funerals.
NARRATOR: The police launched an investigation. Todd Willingham was the primary suspect.
MAN: You have got to account his actions before and after. You have got to account his actions during the fire and things like that that makes the whole story, not just one little segment of it. It's every bit of the story.
NARRATOR: In the 12 years since Willingham's conviction, one fact had remained unquestioned: The fire was an arson.
MAN: The burn pattern is unusual to a normal fire burn.
NARRATOR: But, during those years, there had been a dramatic change in the science of arson investigation.
John Lentini is at the top of his field, one of a small group who reinvented the science of arson detection.
JOHN LENTINI, arson expert: So many determinations were based on hunches and feelings. And these guys, they talk about, oh, you have got to get in there and feel the beast. Oh, I'm just embarrassed for the profession that this is the way people evaluate physical evidence.
NARRATOR: The change in arson science began when scientists set their own fires and studied how they burned.
DR. GERALD HURST, arson expert: That was the first time science was ever really introduced into the mainstream of fire investigation.
NARRATOR: Like Lentini, Dr. Gerald Hurst was one of the new fire scientists. For years, Willingham supporters had tried to enlist Hurst's help. They finally gave him the state's arson report only weeks before the scheduled execution.
DR. GERALD HURST: Taking a look at the photographs and video and testimony and fire investigation report, it became apparent that we were dealing with a fire which had gone to flashover.
NARRATOR: Flashover, the instant ignition of all combustible material in a room.
DR. GERALD HURST: The flashover had left natural patterns on the floor that all post-flashover fires tend to leave behind. And these had been misidentified as floor patterns, and thus the fire had been labeled an arson.
GWEN IFILL: Willingham's family asked a Texas court to reopen the case and determine whether he was wrongfully convicted. A ruling could come later this fall. "Death by Fire" can be seen on most PBS stations tonight.