COLUMBIA — A man on death row for raping and strangling a Clemson University student five years ago is asking South Carolina's top court to throw out his sentence because he claims prosecutors intimidated one of his key witnesses.

Jerry Buck Inman's lawyers will ask the state Supreme Court on Wednesday to toss out his guilty plea and death sentence. Authorities said the 40-year-old with previous rape convictions broke into Tiffany Souers' apartment near campus in May 2006. The engineering student from Ladue, Mo., was found dead by a roommate, with the bikini top used to kill her still wrapped around her neck.

Much of Inman's appeal centers on social worker Marti Loring of Atlanta, who was supposed to testify at sentencing hearings following his September 2008 plea. She had been slated to discuss abuse Inman suffered growing up and his mental health problems.

Loring was not licensed in South Carolina, and during questioning about her credentials, Solicitor Bob Ariail suggested she could face charges for practicing without a license in Inman's case and others she worked on in the state.

Loring then said she felt threatened and wasn't sure if she could properly represent Inman's best interests even after the judge offered her immunity from prosecution.

Inman's lawyer asked for a mistrial, and when that motion was denied he unsuccessfully sought to have Ariail and his other prosecutors thrown off the case.

'It violates the essential demands of fairness for the solicitor, as the one did here, to intimidate a defense expert to essentially remove her as an effective defense witness,' Inman's lawyers wrote in their appeal.

The state attorney general's office said if Loring didn't want her credentials questioned or the suggestion of criminal charges made, she should have gotten licensed in South Carolina instead of assuming her Georgia credentials would be honored. They said questioning an expert's qualifications is a vital step taken by both prosecutors and defense lawyers.

Inman's lawyers also are appealing his guilty plea. Inman wanted to plead guilty to murder and then be sentenced by a jury, but state law does not allow that. During Inman's plea, his lawyers went back and forth with the judge over whether Inman would be allowed to appeal being sentenced by a judge instead of a jury. Inman's lawyers are asking the Supreme Court to weigh in on that as well.

A habitual criminal, Inman spent years in prison for rapes he committed as a teenager in North Carolina and Florida. He had been free from prison for about nine months before Souers' death.

Inman also faces charges in an attempted rape in Alabama and a rape in Tennessee that authorities have said occurred in the days before Souers' death.

After his arrest in Tennessee, a state agent testified that as he told Inman his charges could make him eligible for the death penalty, Inman interrupted the officer. 'That's what I want,' Inman said, according to the agent. 'I killed a 20-year-old college student with everything to live for.'