Lawyers for a man sentenced to death for killing a University of North Dakota student submitted a document Tuesday for what is considered the final step in the legal appeals process, claiming his trial team was ineffective and that the man is mentally disabled.

The 298-page document, a so-called habeas corpus motion, was filed in federal court for Alfonso Rodriguez Jr., who was convicted of kidnapping resulting in the death of Dru Sjodin of Pequot Lakes, Minn. Rodriguez, 58, of Crookston, Minn., is being held on death row at a federal prison in Terre Haute, Ind.

The appeal was filed by attorney Joseph Margulies, a Northwestern University law professor who has represented several death row inmates. U.S. attorneys in the case depicted Rodriguez "as little better than an animal, uncaring and unworthy," Margulies said.

"We now know this carefully scripted tale conceals much and reveals little. Little about the government's case, and even less about Alfonso Rodriguez, was true," the document says. "In the pages that follow, we describe in meticulous detail the difference between what was and what could have been."

Federal prosecutors were not immediately available for comment.

Sjodin was abducted from the parking lot of a Grand Forks shopping mall in November 2003. Authorities say she was raped, beaten and stabbed. A jury sentenced Rodriguez to death on Sept. 22, 2006. It was the state's first federal death penalty case and resulted in tougher laws for sex offenders.

Rodriguez earlier lost an appeal with a three-judge panel of the 8th U.S. Circuit Court of Appeals, in a 2-1 vote. Rodriguez asked for a hearing in front of the full circuit court, which was denied. The U.S. Supreme Court refused to hear the case.

Margulies said the previous legal team failed to uncover that Rodriguez is mentally disabled.

"And were there no more to learn about Mr. Rodriguez than the fact that he is retarded that would be enough," the lawyer writes. "Because the law accepts what no civilized society should question: we do not kill the mentally retarded."