OKLAHOMA CITY (KFOR) – The attorneys for Richard Glossip filed a clemency petition Friday with the Oklahoma Board of Pardon and Parole to secure a new evidentiary hearing before his September execution.

“It’s not a typical clemency petition where someone says, ‘You know, I’ve changed’,” said his pro-bono attorney Don Knight, while adding that Glossip had no prior criminal history. “He’s also an innocent man, and our clemency petition talks about all the problems with this case that led to his being wrongfully convicted and spending the last 25 years on death row.”

Glossip has been on death row since 1997, following his conviction for killing his boss, Barry Van Treese, the owner of the Best Budget Inn.

His attorneys maintain that he was convicted on several adverse factors, including a negligent police investigation and “unvetted, unreliable evidence.”

The newly filed petition centers on new evidence, including testimonies from unheard witnesses and a handwritten note from the admitted killer, Justin Sneed, and comes as the state makes its fourth attempt to execute Glossip.

Sneed’s 2007 statements, in his own handwriting, regarding Glossip’s case saying: “I think you know were [sic] I’m going it was a mistake

In 2007, three years after he testified against Glossip, Sneed wrote to his own attorney, saying his testimony was a mistake.

“He [Sneed] tried as best he could to get somebody’s attention,” Knight said. “He wanted to tell the truth [but] he was shut down by his lawyer.”

“We have a lot of new evidence we have since we have since 2015 found about 17 new witnesses that tell the full story here,” he continued.

The petition also follows a lengthy supplement to a June report released on Aug. 9 by law firm Reed Smith revealing additional information while renewing concerns about witness testimony and mishandling of evidence.

Glossip’s attorneys were also joined by dozens of Oklahoma lawmakers who previously pushed for a hearing based on what they claim is new evidence of his innocence.

The group, which included Representative Kevin McDugle, asked the Attorney General to approve an evidentiary hearing for the presentation of new evidence.

The Attorney General declined that request; his office also declined KFOR’s request for comment Friday.

“I’m very disappointed in our AG’s office that we can’t take a step back and admit when we’re wrong or at least stop taking the hard line that, ‘Hey, there’s nothing to see here,’” said McDugle.

“I’m hopeful that we can get to a point that the Court of Criminal Appeals will do the right thing on behalf of Oklahoma. And let’s go to this hearing and allow everybody to bring their evidence to the table. And I guarantee you, if they do that, Richard Glossip walks out a free man and should have never, ever been on death row or even in prison in the state of Oklahoma,” he added.

“Every Oklahoman should say and demand, ‘Hey, we want the truth here before we execute a guy,’” said Knight. “We have a chance still to get this right.”

Glossip is set to be put to death on Sept. 22, but he has a clemency hearing before the Oklahoma Pardon and Parole Board.