A new documentary is injecting itself into the presidential campaign: “Incendiary: The Willingham Case,” which shines a spotlight on the Texas justice system — and the governor who signed off on the execution of a convicted arsonist whose guilt has been called into question.

The film, which opens at Washington’s E Street Cinema Friday, focuses on a 1991 house fire that killed three small girls. Their father, Cameron Todd Willingham, was convicted their murder, and was executed in 2004. Gov. Rick Perry, R-Texas, signed his death warrant.

As documented in The New Yorker by David Grann in 2009, Willingham’s conviction was based in large part on arson science that has since been widely debunked. Just days before a state-appointed investigatory committee was poised to issue a critical report on the case, Perry replaced the chairman and two other members of the state Forensic Science Commission.

“The cover-up is worse than the crime,” filmmaker Steve Mims told us on ABC’s “Top Line” today. “People can make their own judgment about what people did… But you can look at it now, and you can say that from the day [Perry] fired three people from this commission two days before a presentation of the evidence, all the way to the attorney general’s ruling, which was July the 29th of this year — there’s been a real process in place that seems to be to slow it down, and then eventually to make it go away all together.”

A central component of the film, co-director Joe Bailey Jr. told us, is how the justice system reviewed procedural questions but never the science behind the evidence, as Willingham’s case made its way through Texas courts.

“As citizens, we assume that if a case has gone through the appellate process all the way through that high level of scrutiny has been placed on the case,” Bailey said.

“But what people don’t really realize outside of the legal community is that appeals courts don’t look at factual evidence, and they don’t look at the original evidence. The trial jury were the only people to look at whether this was an intentionally set fire.”

Mims and Bailey don’t make a clear-cut case establishing Willingham’s innocence. In the film, Willingham’s own defense attorney is among those quoted as insisting on his guilt.

Said Bailey: “That’s one of the things that fascinated us about the case originally, is that we have this sort of growing consensus, unanimous consensus from the scientific community that there’s no evidence of arson, that [no] crime was committed. And then you have all these people that were close to the case that have no reservations about the conviction or about the execution. And that contrast was really fascinating to us.”

For his part, Perry has called Willingham a “monster,” and has suggested that claims to the contrary are anti-death penalty propaganda.

He said at a Republican debate earlier this month that he’s “never struggled” with questions of the guilt of any of the 234 people put to death during his time as governor – the most executions a governor has presided over in modern American history.

Perry’s capacity to stop the execution was limited. But Bailey pointed out that he could have issued a 30-day stay of execution if he thought enough flags had been raised to merit reconsideration.

“In the Texas system, the governor is sort of a failsafe for capital cases,” he said.