(CNN) -- Attorneys are set to ask a Pennsylvania judge Thursday to call off the execution of a death row inmate, arguing prosecutors withheld evidence that he was sexually abused by the man he later beat to death with a tire iron.
Terrance Williams, 46, is scheduled to be executed on October 3 for the 1984 slaying of Amos Norwood.
Defense attorneys argue that the jurors who convicted Williams more than 25 years ago were told that it was a robbery-homicide case and never learned of the alleged sexual abuse.
A sworn statement from the case's primary witness -- who is serving a life sentence for his involvement in the murder -- supports that allegation.
Marc Draper has said the prosecution at the time pushed him not to disclose that Williams was routinely sexually abused by Norwood, and that the abuse was Williams' primary motive to kill Norwood. He is expected to testify Thursday.
The sexual abuse allegedly began when Williams was 6 years old, according to his attorneys.
"Several jurors now say they would have voted for life in prison without the possibility of parole instead of death if they had known this important information," Williams' attorneys said in a statement last month after his execution date was set.
Philadelphia District Attorney Seth Williams has said the abuse allegations are hearsay and "a last-ditch effort to escape punishment."
"In the 28 years since the murder of Amos Norwood these new allegations only came to light just a few months ago, and (Williams) is not the one making the allegations. ... Not once has Williams actually testified under oath about all the abuse he allegedly suffered," the district attorney said in a statement Monday.
Announcing the scheduled execution last month, Pennsylvania Gov. Tom Corbett's office described the brutal Philadelphia killing.
Williams and Draper led Norwood to an area near a cemetery, forced him to lie on the ground, tied him up, gagged him and stole his valuables, the governor's office said in a statement.
"Williams and Draper repeatedly beat the man with a tire iron and a socket wrench and then drove away in the victim's car. Williams later returned and burned Norwood's body," the statement said.
Since the execution date was set, there have been a number of high-profile supporters calling for clemency in the case, including Pennsylvania Attorney General Linda Kelly. More than 360,000 people have signed an online petition asking authorities to spare Williams' life. Norwood's widow has also asked for the execution to be called off.
But Norwood's daughter wants the execution to go forward, the Philadelphia district attorney's office said Monday.
The state's Board of Pardons on Monday failed to reach the unanimous agreement required to recommend clemency. Three members of the five-person panel voted in favor of asking Corbett to consider granting clemency. But two other board members voted against the petition.
That means Thursday's hearing could be Williams' last chance to make his case.
Judge M. Teresa Sarmina, who will preside over the hearing, has the authority to grant a stay of execution should she be convinced by the defense that prosecutors withheld evidence in the 1986 trial.
CNN's Adam Reiss contributed to this report.