People who escape fatal fires with their lives may face a tangle of emotions: fear, regret, relief.
In many cases, they also face criminal charges.
If just 5 percent of the nation's half-a-million yearly structure fires are suspicious, Lentini said, then that means 25,000 chances to mistakenly charge someone with arson.
"And if they [prove a crime took place] with bad evidence, and the jury believes that it's a set fire, many times there is no doubt about who did it," he said.
Kristine Bunch was convicted by a jury in 1996 of setting a fire in her Indiana trailer that killed her 3-year-old son. She received concurrent sentences of 50 years for arson and 60 years for murder.
"This is a woman who has no prior criminal history ... no arrest record ... no psychiatric history," said Jane Raley, senior staff attorney at the Center on Wrongful Convictions at Northwestern University School of Law. "There was nothing here."
Raley is working to get Bunch, 36, a new trial. "There is no motive," Raley said. "Why would someone like Kristine do this?"
Lentini questioned the evidence against Bunch.
"I can turn just about any fire into an arson fire if that's what I want to do," he said.
Arson: Conducting a Fire Test
We brought Lentini to the Fire Science Program at Eastern Kentucky University, where technicians conduct fire tests in a bunker set up with rooms of ordinary furniture.
Fires are set in the bunker not with gasoline or other flammable liquids but with just a spark, as if from a burning cigarette.
"We are hoping to generate some of the artifacts that people in the past have called evidence of arson," Lentini said.
Among those whom Lentini counts as having believed misguided arson evidence in the past is ... John Lentini.
Twenty years ago, Lentini got a life-changing lesson in arson fires. Back then, he was convinced that a man named Gerald Lewis had killed his pregnant wife and four children by setting a fire with gasoline in Jacksonville, Fla.
"I was scheduled to be deposed the next morning for the prosecution," he recalled. "I was going to help them send Gerald Lewis to Old Sparky [the electric chair]."
But before he testified, Lentini had a chance to test Lewis' claim that the blaze began by accident when his couch caught on fire.
Arson: The 'Lime Street Fire Test'
Lentini's test is now commonly called the "Lime Street Fire Test." To Lentini's surprise, the fire in the test left behind the exact same signs as if it had been started with gasoline, even though none was used.
"It was an awakening," Lentini said.
Which is why Lentini is now driven to bring hard science into what traditionally has been seen as the "art" of fire investigation.
"I think when they said ... 'art,' I think what they meant was luck," Lentini said.
Back at Eastern Kentucky University, investigators began their fire experiments, with cameras and thermal imaging sensors recording every moment.
The tiny couch fire grew steadily as a layer of hot dense smoke formed on the ceiling. The sensors showed how hot it was. Temperatures reached about 1,200 degrees. Soon, blazing hot gas started to descend.
Just minutes after the fire was started, the hot gases suddenly ignited, and the room exploded.
This is a phenomenon known as "flashover."
"Flashover is a transition point where you go from having a fire in a room to a room on fire," Lentini said.
Arson: Burn Patterns and Points of Origin
But what you see after a fire has exploded into flashover is even more important to our story. Lentini guided us through the ruins after the fire was out.
"If you see a pattern on the couch, that looks like it's where it started," Lentini said. "'Cause there's a 'V' [a V-shaped burn pattern] over there, and there's a 'V' over here. You say, 'Well, that could be two points of origin.'"
The appearance of multiple points of origin in a fire has traditionally been regarded as "slam-dunk" evidence of arson, Lentini said.
It was such a slam-dunk that helped put Bunch in the slammer. During Bunch's trial, the prosecution used photos showing burn patterns as evidence of multiple places of origin.
"That is 100 percent inaccurate," said Raley, who is working for a new trial. "One hundred percent wrong. One hundred percent fiction."
When Bunch was convicted in 1996, Raley said, flashover and the science of arson were not well understood. Bunch has now served 14 years in prison and has no hope of parole for at least 12 years.
The prosecutor in Bunch's case declined our request for an on-camera interview, but he maintained that the jury made the right decision. He said that Bunch's behavior was questionable and that she made many contradictory statements during numerous police interviews. The jury made its decision on matters that go beyond the science alone, he said.
There wasn't much left of Bunch's trailer after fire swept through it, killing her son, Tony, 3, in June 1995. What was left, according to fire investigators at the time, was unmistakable evidence of arson.
"The arson conclusion was made within two hours of the investigators arriving at the trailer," Raley said. "The first investigators arrived around 8 o'clock in the morning. By 10 o'clock in the morning, there had already been a conclusion."
That conclusion was that Bunch had poured accelerant in her son's bedroom, touched off the fire and let him die. "I am never going to stop fighting, never going to stop trying to prove that I didn't do this," Bunch said.
Arson: 'Their Theory Is Impossible'
Prospects for a new trial for Bunch may depend on one woman, Jaime McAllister, an expert in the emerging field of combustion science. McAllister's opinion about the prosecution's original arson case can be summed up in four words.
"Their theory is impossible," she said.
An autopsy report on the little boy's body showed he died with 80 percent carbon monoxide in his blood. That's an impossibly high number, McCallister said, if the fire had been set in his room.
"You couldn't breathe in that amount of carbon monoxide and get to that level of 80 percent before you would die from the heat," McAllister said.
Tony Bunch was dead, she said, long before the flames got to him.
Basic science suggested the fire started in an unventilated place, like in the space between the ceiling and the roof, where there were electrical wires and a malfunctioning light, McAllister said.
A short in the wires could have overheated the ceiling tiles.
"As that smoldering occurs, it produces a lot of products, like soot and carbon monoxide," McAllister said. "And they would start to leak out in the room."
Arson: Wrongful Conviction?
In her theory, little Tony passed out from breathing carbon monoxide. The fire grew. Ceiling tiles broke down and fell. Fed by more oxygen, much thicker, hotter smoke billowed into the room.
"Very quickly, he is going to inhale those products, and he is going to die very quickly from those products," McAllister said.
For Bunch's lawyer, the new toxicology evidence leads to only one conclusion.
"The fire could not have started in the living room, it could not have started in the bedroom," Raley said. "So we know that the fire could not have happened the way the state claims. ... It just can't happen."
But if the fire did not happen as the prosecution claimed it happened, why wouldn't a new trial be guaranteed?
"Well," Raley said with a sigh, "it's always difficult to unravel a wrongful conviction."
Decatur County, Ind., prosecutor William Smith said he believes the "new" science was already rejected by the jury.
He said Raley just wants to substitute her expert's opinions for that of the jury.
The court ruling could come at any time. This first appeal is the least likely to succeed, said Raley, who vows that she is prepared to keep going to higher courts in an effort to get Bunch a new trial.