CORSICANA — More than a decade after Cameron Todd Willingham was executed for the arson murder of his three young daughters, new evidence has emerged that indicates that a key prosecution witness testified in return for a secret promise to have his own criminal sentence reduced.

In a previously undisclosed letter that the witness, Johnny E. Webb, wrote from prison in 1996, he urged the lead prosecutor in Willingham's case to make good on what Webb described as an earlier promise to downgrade his conviction. Webb also hinted that he might make his complaint public.

Within days, the prosecutor, John H. Jackson, sought out the Navarro County judge who had handled Willingham's case and came away with a court order that altered the record of Webb's robbery conviction to make him immediately eligible for parole. Webb would later recant his testimony that Willingham confessed to setting his house on fire with the toddlers inside.

Jackson's handling of the case is now under investigation by the State Bar of Texas, following a formal complaint of prosecutorial misconduct last summer. That grievance asked that Jackson be sanctioned or even prosecuted for falsifying official records, withholding evidence and obstructing justice.

Regardless of when Jackson would have learned of a possible deal, he would have been legally bound to disclose any such favorable treatment of a witness to the defense. For Willingham — who maintained his innocence until he was executed in 2004 — the revelation might have been sufficient grounds for a new trial.

To death penalty opponents, Willingham's case is among those that have come closest to proving for the first time in the modern era of capital punishment that an innocent person has been put to death in the United States.

In an e-mail, Byrne said he could not comment on any of the specific allegations against Jackson, because they involved pending litigation. But he added, "We are confident that a Texas jury who hears all of the evidence in this case will find that Mr. Jackson has done nothing inappropriate."

Jackson did not personally comment in response to e-mails or telephone calls requesting he address the matter.

Jackson has long denied that the state cut any sort of deal with Webb for his testimony. But Jackson recently amended his account, telling the Texas bar that he had intervened on Webb's behalf after Webb's attorney told Jackson in 1996 that she believed her client's conviction should have been for the lesser charge. Webb's attorney said she based this belief on her negotiations with Jackson's boss, the district attorney, Jackson said.

At the time of the fire that erupted in the small frame house Willingham shared with his wife and three daughters, he was 23 years old, an out-of-work car mechanic with a volatile marriage and a local reputation as something of a troublemaker. He said he awoke from a nap to find the home so filled with smoke and flames that he could not locate his sleeping children and was barely able to stumble out of the house alive.

In two days of interviews recently with the Marshall Project, Webb gave the most detailed account to date of how he came to testify against Willingham. He said that Jackson threatened him with a life sentence in the robbery case — a possibility under Texas law because Webb had several prior convictions — unless he testified.

"I did not want to see Willingham go to death row and die for something I damn well knew was a lie and something I didn't initiate," Webb said.

"I lied on the man because I was being forced by John Jackson to do so," Webb said. "I succumbed to pressure when I shouldn't have. In the end, I was told, 'You're either going to get a life sentence or you're going to testify.' He coerced me to do it."

During Willingham's three-day trial in August 1992, Jackson pointedly asked Webb on the witness stand whether he had been promised a lighter sentence or some other benefit for his cooperation. Webb told the judge and jury that he had not.

Documents published last year by the Marshall Project and The Washington Post showed that during and after Webb was in state prison, he received thousands of dollars in aid from a wealthy local businessman, Charles S. Pearce Jr. Webb said in interviews that Pearce had helped him at the behest of Jackson; Patrick C. Batchelor, the district attorney; and the county sheriff. Jackson later denied that claim, saying that any support Pearce gave "had no connection" to Webb's testimony in the Willingham case.

But in his formal response last September to the misconduct complaint, Jackson revised his long-standing assertion that Webb had not cut any sort of deal in return for his testimony.

This time, he said that after receiving correspondence from Webb questioning his sentence, he turned to Webb's former defense attorney, April Sikes, who had worked with Jackson as a prosecutor before joining the defense bar. Sikes "indicated to me that she believed Webb's conviction should be a second-degree felony because he cooperated in the Willingham case," Jackson said. He added that this was based on "her recollection of negotiations with Patrick Batchelor."

Jackson said that he "was not the prosecutor responsible for the Webb case," despite the fact that he appeared in court at Webb's guilty plea. He was merely standing in for Batchelor on that day, he said, but "had no input into the plea agreement with Webb ... or the drafting of the judgment."

Legal experts say that even if Jackson did not make a deal with Webb himself and was unaware of one at the time of Willingham's trial, he would still have been obligated to report to Willingham's defense attorney in 1996 if he believed one had been made.

"The prosecutor's office had a duty to disclose the agreement," said Stephen A. Saltzburg, a professor at the George Washington University Law School. "Whenever that was discovered, it should have been disclosed."

In his response to the bar complaint, Jackson said that he tried to help Webb get out of prison early and orchestrate his transfer back to the county jail but insisted that he had done so to try to protect Webb from unspecified threats of "murder, injury, or threats by the AB [Aryan Brotherhood] or Willingham sympathizers." Jackson said in his response to the bar, "In my opinion this is proper conduct and certainly not evidence of a pre-trial agreement, inducement of Webb to give perjured testimony, or other wrongdoing."

A letter that Webb said he sent to Jackson on June 24, 1996 - a signed, carbon copy of which he kept in his voluminous record of prison correspondence and provided to the Marshall Project - indicates that Jackson had promised to help Webb.

"Dear John," Webb wrote. "Recently, as I was going over my case notes, I noticed that you had told me that the charge of aggravated robbery would be dropped, or lowered, to robbery. ... You told me this would be done before my transfer to TDC [Texas Department of Corrections]." Webb was transferred from the Navarro County Jail to the Texas prison system in the fall of 1992.

Webb explained that prison officials were still calculating his sentence as an aggravated offender, a first-degree charge. "There may be an error in the paperwork, or in TDC's computer and they are not following the agreement we entered," Webb wrote.

In what appears to have been an attempt to pressure Jackson, Webb said that if Jackson could not "take care of it on your own," Webb might file a court motion to request the adjustment - a move that might have brought his purported deal with Jackson to light as Willingham was appealing his death sentence.

Webb had written weeks earlier to the Navarro County judge who had handled his case and Willingham's, Kenneth "Buck" Douglas, asking to be moved back to the Corsicana jail or into protective custody and writing that "the state offered me certain benefits in exchange for my testimony."

Webb also addressed that document to Jackson. In the June letter, he went further, pressing Jackson to check whether Webb's case file reflected a conviction for aggravated robbery and, if so, to seek a court order changing the record "to clarify any problems."

Within three weeks after Webb's letter, Jackson did just that: He first persuaded Douglas to enter a new judgment in Webb's case, officially recording his conviction as second-degree robbery.

Jackson then wrote to the Texas Board of Pardons and Paroles, appending the judgment and saying the court order confirmed that Webb had been convicted of the lesser charge. The result was that Webb, to whom Jackson sent a copy, became immediately eligible for parole.

Webb's letter to Jackson was never placed in the public file of Webb's case or the district attorney's internal file on the case, which was turned over to the nonprofit Innocence Project in response to a disclosure request.

Although Jackson declined to answer questions about whether he received Webb's letter and what he might have done about it, in his response to the Texas bar complaint, Jackson said he sought the order from Douglas "upon the request of Johnny Webb." Jackson also said that in July 1996, the issue of the "inconsistent judgment" was raised "most likely through letters from Webb."

In Jackson's response to the bar complaint, he also provided other details that seem to jibe with Webb's account.

Jackson acknowledged that around the time Webb went off to state prison in 1992, he checked with a court clerk about Webb's conviction and was surprised to see that the trial judgment was contradictory. It listed robbery instead of aggravated robbery as the crime to which Webb had pleaded but included the penal code for aggravated robbery nonetheless.

An undated note that was discovered in the clerk's file of the case years later seemed to indicate that Jackson had tried to use the ambiguity in Webb's favor: It said that if a Texas corrections official called for clarification, "tell them ROBBERY with No Deadly Weapon Used. . . . This is what John Jackson wants it to be."

Jackson has denied that he wrote the note or asked the court clerk to put such a note in the file.

"As a matter of due process, Jackson's alleged unawareness of the deal at the time of the trial would not matter," said Bennett Gershman, a law professor at Pace Law School in White Plains, N.Y., and a national expert on the ethical and legal duties of prosecutors. "He still would be deemed responsible for the nondisclosure."

Webb regrets his decision in 1992, saying that if he had refused to testify and gotten a life sentence, he probably would have been paroled after 20 years. "As it is," Webb said, "I'm stuck in this Willingham thing for the rest of my life."

This article was originally written and reported by Maurice Possley for The Marshall Project, a nonprofit news organization focused on the U.S. criminal justice system. You can sign-up for their newsletter, or follow The Marshall Project on Facebook or Twitter.