Prosecutors in Corsicana, about 60 miles south of Dallas, have insisted Willingham's conviction and execution was proper, and the State Fire Marshal's Office has stood behind the arson finding.
Texas Forensic Science Commission chairman John Bradley said the board didn't plan to make a decision Friday and the session was an opportunity for members to ask questions. The commission invited four scientists to testify: Craig Beyler of Baltimore, John DeHaan of California, Thomas Wood from Houston and Ed Salazar of the state Fire Marshal's Office.
Beyler is among several experts who have challenged the conclusion that arson caused the 1991 fire that killed Willingham's three daughters. The chairman of the International Association of Fire Safety Science and one of the foremost experts in the field, Beyler wrote in a 2009 report that investigators didn't follow standards in place in 1991 and didn't have enough evidence to make an arson finding.
The opinions of a state fire official in the case were "nothing more than a collection of personal beliefs that have nothing to do with science-based fire investigation," Beyler wrote.
He was scheduled to testify before the commission in 2009, but Bradley canceled that meeting in an effort to close the case and have the panel conclude investigators didn't commit professional misconduct in the case. Other members of the commission rebuffed Bradley's efforts, leading to Friday's hearing.
Beyler insisted Friday that the cause of the fire should have been listed as undetermined.
"I haven't changed my opinion in the year and a half since I wrote the report," he said.
Bradley said he wasn't quibbling with Beyler's opinion but said he believed the investigators "did the best they could given standards at the time."
"I think we'll differ on that," Beyler responded.
Willingham always maintained his innocence, including in his final statement from the death chamber gurney -- an obscenity-filled diatribe aimed at his ex-wife. She has said he confessed his guilt to her when she met with him days before his execution, but Innocence Project lawyers say her story has changed over the years.
Death penalty opponents have aimed to have the Willingham case become the first one in which a prisoner was formally declared wrongfully put to death.
The forensic commission's involvement became politically charged after Republican Gov. Rick Perry removed three members in 2009, days before they were to review reports casting doubt on Willingham's guilt. Bradley has been an ally for Perry in trying to close the inquiry.
The Innocence Project has objected that two arson investigators who testified on its behalf at an October court of inquiry about the Willingham case, Gerald Hurst and John Lentini, were "notably absent" among investigators the commission invited to Friday's meeting.
The October hearing was cut short by an appeals court after prosecutors successfully challenged the objectivity of the judge holding it because he'd received an award from an organization that opposes the death penalty.
Willingham's defense didn't include a fire expert to counter the state's witnesses because the one hired by his attorney also said arson started the fire.