Fire Expert: How I Nearly an Sent an Innocent Man to the Electric Chair

May 6, 2010— -- John Lentini, one of the nation's leading arson experts, had a life-changing experience in arson fire investigations. Twenty years ago, he was convinced that a man named Gerald Lewis had killed his pregnant wife and four children by setting fire to their home in Jacksonville, Florida. Before he testified for the prosecution, Lentini had a chance to test Lewis' claim that the blaze began by accident when his couch caught on fire. It changed his view of arson investigations forever. Here is his own description of what happened:

My Lime Street Epiphany

When I was first contacted by Duvall County, Florida prosecutors, it was with a request to review the chemical analysis of fire debris in a multiple fatality fire. The state's chemist said he had detected gasoline in some critical fire debris samples. When I reviewed the data, however, I did not see the gasoline, so I sent it to 10 colleagues, who also disagreed with the gasoline determination.

Watch the "20/20" investigation into arson fires Friday at 10 p.m. ET

I was next asked to review the fire scene inspection report prepared by a fire investigator in the Jacksonville Fire Department. I thought his report looked pretty reasonable. I thought that he had developed a sustainable determination that the fire was intentionally set using flammable liquids. Because of the lack of a credible laboratory report, however, the prosecution team decided it needed something more.

The "something more" was a test fire conducted in a house two doors down with the same floor plan, which we outfitted with the same furnishings as the house where the people died. The two scientists (myself and another well-known fire scientist) leading the experiment both believed that flashover, a transition point at which heat causes almost everything in a room to catch fire, might be achieved in 15 or 20 minutes. Instead, it took just over four minutes. This added much credibility to the defendant's version of events.

I had been scheduled to sit down with the defendant's lawyer the next day for a deposition (Florida is one of the few states where all witnesses in criminal proceedings can be questioned under oath before trial). But I told the prosecutors, who had witnessed the test fire, that based on the test results, I was no longer able to state that I thought the fire was intentionally set. I had come within 24 hours of giving testimony that could well have sent an innocent person to Florida's electric chair. Needless to say, I was chastened by the experience. My professional life was never the same again.

Although the prosecutors were relieved to have avoided bringing a questionable case to trial, I was derided and demeaned by many fire investigators who would have gone forward with the case even with the test results we had, based on their visual observation of the "pour patterns" on the floor.

I made a videotape of the Lime Street fire investigation and showed it to some colleagues at the next meeting of the International Association of Arson Investigators (IAAI). One of those present, IAAI President David Smith, told me he had a similar case in Arizona and asked if I would be interested in reviewing the case for the court. I saw the same kind of flawed reasoning used to determine arson in that case as well. Of course, this got me deeper in trouble with the proponents of "traditional" fire-cause determination, but I held my ground.

After this experience, I counted only those investigators favoring a scientific approach to fires among my friends, but over the years that cadre has grown, while the number of proponents of the old way of doing things has shrunk. The great scientist Max Planck may have said it best: "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it." This quotation is sometimes paraphrased more succinctly: "Science advances one funeral at a time."

For a more detailed account of the Lime Street Fire Investigation CLICK HERE and select "The Lime Street Fire: Another Perspective."

Watch the "20/20" investigation into arson fires Friday at 10 p.m. ET