BUFFALO, Mo. (AP) — Defense attorneys say evidence was withheld that would have helped prove the innocence of a Missouri man convicted of killing his wife after her Christmas Day 2006 death initially was ruled a suicide.

At issue is testing on the robe that Bradley Jennings was wearing when 39-year-old Lisa Jennings died at the couple's home in Buffalo, about 35 miles northeast of Springfield. The Springfield News-Leader reports that the defense didn't learn until December 2015 that the robe tested negative for gunshot residue.

Jennings, now 61, is eight years into a 25-year sentence. His defense wants him to be freed or to get a new trial. A hearing is set for this week.

The Dallas County coroner and sheriff's office initially found that the death was suicide. But two months later, Lisa Jennings' younger sister went to the Springfield office of the Missouri State Highway Patrol and met with a sergeant who decided to re-investigate, leading to the determination that blood spatters on Lisa Jennings' hands were inconsistent with a suicide.

Records show Jennings voluntarily cooperated, agreeing to be interviewed without a lawyer present and providing the unwashed robe so it could be tested.

The testing led to the determination that blood on the robe could only have come from a high-velocity gunshot wound. Jennings, however, told authorities that he held his wife's bloody body after she shot herself following an argument. The couple had been married 18 years and had two children. Lisa Jennings also had a child from a prior marriage.

During the trial, the prosecutor suggested that Jennings — who did not testify — killed his wife while wearing the bathrobe, then changed clothes and washed up to remove gunshot residue from his hands before police arrived. The prosecutor also suggested that the reason Lisa Jennings had gunshot residue on her right hand was not because she fired the weapon, but because she was near Brad Jennings when he fired it.

Jurors heard nothing about the lack of gunshot residue. In fact, Jennings' defense lawyer, Darrell Deputy of Lebanon, in his closing argument in 2009 pleaded with jurors to ask themselves why patrol investigators did not conduct such a test — apparently unaware that they actually did.

"I would have done it in a heartbeat," Deputy told jurors, according to a trial transcript.

The evidence was only uncovered after Bradley Jennings' sister hired an investigator. Robert Ramsey, a St. Louis attorney who now represents Jennings, has filed a request for a judge to vacate the prior conviction. Ramsey argued in a petition that it was "clearly a close case" and that the suppressed gunshot residue test shows that his client is "actually innocent."

In recent legal filings, the Missouri Attorney General's Office has said prosecutors did not know at the time of the trial that the test was done and didn't know the results.