The long-running effort to bring clarity to the January 1989 murder of then-Oregon Department of Corrections Director Michael Francke took a new turn this week when the Oregon Innocence Project weighed in on behalf of Frank Gable, the man convicted of Francke's murder.

In a 27-page friend-of-the-court filing, the Oregon Innocence Project urged U.S. District Court in Portland to consider that seven prosecution witnesses who played a role in Gable's conviction have recanted.

Although Innocence Projects around the country have made headlines for using DNA evidence to clear wrongly convicted suspects, the Oregon Innocence Project is arguing in its brief that police used a variety of techniques to coerce witnesses to implicate Gable and help sentence to life in prison.

"At least seven prosecution witnesses in this case initially denied any knowledge about the murder of Michael Francke and then implicated Petitioner Gable after prolonged police interrogation that involved the use of false evidence, threats, excessive polygraphing, and incentives. All seven of those witnesses later recanted their incriminating statements," the brief says.

"OIP urges this Court to consider the recantations, whether by affidavit or at an evidentiary hearing, in light of the circumstances giving rise to the recantation as well as the circumstances giving rise to the testimony now asserted to be false."

Francke's murder marked an extraordinary chapter in Oregon history: the prisons boss was stabbed to death outside his office in a well-lit parking lot; the crime came at amid his efforts to both address corruption in his agency and a troubled effort to expand Oregon's prison system.

The investigation of Francke's death proceeded slowly. Not until 15 months after Francke's death did a grand jury indict Gable, then a 30-year old Salem ex-con. Investigators never found eyewitnesses nor the murder weapon, which contributed to doubts about whether Gable killed Francke. He was nonetheless convicted and sentenced to life in prison. His conviction was subsequently upheld on appeal.

But in October 2014, Nell Brown, a lawyer in the federal public defender's office filed a 198-page brief arguing that the prosecution of Gable was badly flawed. Brown and her investigators had spent years reviewing the case and re-interviewing the witnesses who testified against Gable.

Now, her former boss, longtime federal public defender Steven Wax, who heads the Oregon Innocence Project, which is program of the Oregon Justice Resource Center, is adding the weight of his organization to Brown's criticism of the case against Gable.

Wax's brief, which was first reported by the Portland Tribune, describes several cases around the country in which police tactics have generated false testimony and asks the court to evaluate Gable's conviction in light of increasing evidence of the credibility of coerced testimony.

"OIP requests the Court consider the specific interrogation techniques used on independent witnesses who initially denied any knowledge of the murder and have now confirmed that their trial or grand jury testimony implicating Mr. Gable was false and came only as a result of police interrogation tactics," the brief says.

The Oregon Department of Justice, which is tasked with defending Gable's conviction will now have a chance to respond to Gable's advocates.