The government's key evidence in the case was a pattern of burning that the prosecution argued indicated three separate fires -- and arson.
"I think there was an electrical fire," said Lentini, who was part of Severns' defense team. A frayed cord on a fan in the gun shop's cluttered workshop probably ignited the blaze, Lentini thinks. Nearby aerosal cans could have exploded -- setting off multiple fires.
Prosecution experts said that was impossible, and the jury convicted Severns.
"I walked into trial, maybe even cocky," Severns told ABC News in a phone interview from prison. "I don't know. I thought this is nuts, we'll be able to tell the story and it's no big deal. It just didn't turn out that way... When I heard 'guilty,' I shook and my legs gave way."
But a few months later, Lentini discovered a videotape that he claims the prosecution should have known about.
The video showed a test fire involving aerosol cans. Sure enough, as the cans heat up in the video, they burst and fly around the room. Slowing the tape shows clearly that the flaming cans touch off new fires wherever they land.
"The fact is [the prosecution] misrepresented the science during [Severns'] trial, and they ridiculed me for trying to bring it up," said Lentini.
Armed with the tape, Severns' lawyer appealed. But the judge said the video would have made no difference to the jury and denied the appeal.
If the tape had been shown at trial, Sue Severns said, "the outcome would be completely different. The jury would have been able to see a TV show, a video, a movie of how the aerosol cans can create the appearance of multiple origins ... It would have been a wonderful testament."
The federal prosecutor in the case, who declined ABC News' requests for interview, offered Severns a plea deal prior to his conviction.
Severns said his reason for refusing the deal was simple.
"'Cause I didn't do it!" he said.