Duke was acquitted of malice murder, felony murder, aggravated assault and burglary, but was found guilty of concealing a death. The jury deliberated Thursday afternoon and Friday morning before reaching a verdict after a nine-day trial.
Duke admitted to the Georgia Bureau of Investigation (GBI) that he killed Grinstead in 2017, but during the trial, he said he did not kill her, pointing the finger at his former best friend Bo Dukes.
He was asked during the trial if he killed Grinstead.
"I did not," Duke replied.
Five years ago, Duke told the GBI that he broke into Grinstead's house to steal money for drugs and fatally struck her when she startled him.
"I was stealing from her purse and she snuck up on me," Duke told GBI agents in a video shown to the jury. "She snuck up on me and I hit her. It was reactionary. I ran. I didn’t know what else to do."
Duke told agents he tried calling Grinstead's house from a payphone after he ran, and when she didn't answer he returned to the scene to find her dead. He told investigators: "I can’t lie. I can’t live with myself I’m so sick of this."
But during the trial, Duke said that he was woken up by Bo Dukes on the night of Grinstead's death in 2005 in the mobile home where they were living.
Duke testified: "He said he killed Tara." He said Dukes then showed him Grinstead's purse and wallet.
Dukes was sentenced to 25 years in prison after a jury convicted him in 2019 of helping Duke remove Grinstead's body from the house and burn it in a pecan orchard. Dukes denied killing Grinstead and wasn't charged with murder.
Attorney Philip A. Holloway, who has followed the case closely for years, told Fox News Digital that the jury reached the "appropriate verdict," based on the evidence and testimony presented during the trial.
"I believe that guilt was not proven beyond a reasonable doubt," Holloway said. "I also think that the conviction on count six is inconsistent with the verdicts on the other counts And I also believe it should be dismissed due to statute of limitations. The real question is what does the judge think. We will find that out on Monday."
Monday is when Duke is scheduled to be sentenced.
The Associated Press contributed to this report.