HUNTSVILLE, Texas (AP) — A Texas death row inmate is set to be executed for the abduction, rape and murder of a suburban Houston college student more than 20 years ago, even though he has always maintained his innocence and contends his conviction was based on junk science.

Larry Swearingen, 48, is scheduled to receive a lethal injection Wednesday evening for the December 1998 killing of Melissa Trotter. The 19-year-old was last seen leaving her community college in Conroe, and her body was found nearly a month later in a forest near Huntsville, about 70 miles (110 kilometers) north of Houston.

Prosecutors said they stand behind the “mountain of evidence” used to convict Swearingen in 2000. They described him as a sociopath with a criminal history of violence against women and said he tried to get a fellow death row inmate to take credit for his crime.

Swearingen’s longtime appellate attorney, James Rytting, said he would ask the U.S. Supreme Court to halt the execution, arguing that lower courts “have failed to take into account the considerable amount of evidence of innocence.” Swearingen, who is also represented by the Innocence Project, has previously received five stays of execution.

Appeals courts and the Texas Board of Pardons and Paroles declined to stop the execution. If it happens, Swearingen would be the 12th inmate put to death this year in the U.S. and the fourth in Texas.

Kelly Blackburn, the trial bureau chief for the Montgomery County District Attorney’s Office, which prosecuted Swearingen, said Swearingen’s efforts to discredit the evidence have been unsuccessful because “his experts’ opinions don’t hold water.”

“I have absolutely zero doubt that anybody but Larry Swearingen killed … Melissa Trotter,” Blackburn said.

During a 2011 interview, Swearingen told The Associated Press that he was tired of being “demonized” for a crime he didn’t commit.

“We’d all like to know who done it,” he said.

Blackburn said Swearingen killed Trotter because he was angry that she had stood him up for a date. At the time of Trotter’s killing, Swearingen was under indictment for kidnapping a former fiancée.

Swearingen has long tried to cast doubt on the evidence used to convict him, particularly claims by prosecution experts that Trotter’s body had been in the woods for 25 days. Rytting said at least five defense experts concluded that her body was there for no more than 14 days, and because Swearingen had already been arrested by then, he couldn’t have left her body there.

Rytting maintains that a piece of pantyhose used to strangle Trotter was not a match to a piece found in Swearingen’s trailer. He also disputes prosecution experts’ claims dismissing blood found in Trotter’s fingernail shavings, saying the blood, which was determined to not be Swearingen’s, supports the defense theory that someone else killed her.

In letters sent to Swearingen’s attorneys in July and August, the Texas Department of Public Safety said its technicians should not have been as definitive in their testimony about the blood found in the fingernails and the pantyhose match.

The 5th U.S. Circuit Court of Appeals last week turned down Swearingen’s challenge to the blood evidence and pantyhose match, citing the “mountain of evidence” that “seals Swearingen’s guilt for Trotter’s murder.”

Blackburn said Swearingen has tried to get people to lie in order to give him an alibi. After his arrest, Swearingen got another inmate to write a letter Swearingen composed in Spanish that professed to be from the real killer and had it sent to his attorney. In 2017, Swearingen and another death row inmate, Anthony Shore, concocted a plan to get Shore to take responsibility for Trotter’s killing. Shore was executed last year.

Rytting said Swearingen is guilty of doing “some very stupid things,” but prosecutors don’t have proof he killed Trotter.

“Hopefully we are one step closer to giving (Trotter’s family) that justice that they’ve so long waited for,” Blackburn said.