Attorneys for Oscar Smith are urging the courts to take one more look at their client’s case before he is scheduled to face execution later this month.

Smith was convicted of murdering his estranged wife and her two sons from another relationship in 1989. He has spent more than three decades on death row, and his lawyers say he has maintained his innocence the entire time.

In a motion filed Monday, Smith’s defense team says a new forensic analysis has uncovered another person’s fingerprints on the weapon he allegedly used to commit the crime — not his. They also say the investigator who conducted the original forensic analysis with older methodology made “egregious” errors.

Last-minute pleas are common before an execution, given the high stakes. Smith’s attorneys say they are filing this motion now because the software they used to conduct the analysis wasn’t available until this year.

In the past few months, the courts have allowed Smith’s team to conduct a new DNA test on the awl — a sharp object used to poke holes — that prosecutors said at trial was used for the murders. Last week, defense attorneys received the results from the more technologically advanced analysis. They say it “definitively excluded” Smith as the source of the DNA found on the awl.

“The significance of this result cannot be overstated,” they wrote in their motion. “Oscar Smith has, using his new touch DNA technology, demonstrated that he is not the person who used the awl to kill his family.”

Smith had allegedly threatened to kill his wife, Judith Lynn Smith, several times in the months leading up to her death. According to court records, her co-worker at a Waffle House said he overheard multiple phone calls in which he threatened her. He had also reportedly threatened to kill her two sons, Chad and Jason Burnett, from a previous marriage.

The Davidson County district attorney’s office did not immediately respond to a request for comment.

Smith’s execution is slated for April 21. He has not chosen the electric chair, which several other men on Tennessee’s death row have opted for in recent years, out of fear of the potential side effects of the state’s lethal injection protocols. If his execution proceeds, he will be put to death by lethal injection.