Before Texas executed Marvin Wilson last year for the 1992 murder of Jerry Robert Williams in Beaumont, his case generated headlines, reminding the nation of a rather unique corner of death penalty law here.

The standards used to determine whether a Texan convicted of murder is mentally fit to be executed are based in part on the fictional character Lennie from John Steinbeck’s classic novel Of Mice and Men, a fact that enraged the author’s son.

"I find the whole premise to be insulting, outrageous, ridiculous and profoundly tragic,” Thomas Steinbeck said, calling for a halt to Wilson’s execution. “I am certain that if my father, John Steinbeck, were here, he would be deeply angry and ashamed to see his work used in this way."

State Sen. Rodney Ellis, D-Houston, said Wilson’s execution and other cases left him feeling embarrassed for his home state. “It’s junk science. Its not a credible way of making a decision,” he said.

So Ellis filed Senate Bill 750, which would establish new — and, he argues, more scientific — standards to determine when a convicted Texan is too intellectually disabled to face the death penalty. The bill revives a decade-old fight with prosecutors, who argue that the current standards are adequate and that Ellis’ proposal would make it too easy for defendants to make a case that they are mentally retarded and exempt from the death penalty.

“Sen. Ellis’ proposal creates two or three additional bites at the apple for a defendant to show he is mentally retarded, and it skews the process,” said Shannon Edmonds, spokesman for the Texas District and County Attorneys Association.

In 2001, Texas lawmakers approved a bill by then-state Rep. Juan "Chuy" Hinojosa, D-McAllen, now a state senator, that would have implemented new requirements for courts to have independent experts evaluate defendants to determine whether they were mentally retarded. Gov. Rick Perry vetoed the bill. In a proclamation with his veto, he argued that existing safeguards were effective in preventing the execution of the mentally disabled.

The U.S. Supreme Court in 2002 ruled in Atkins v. Virginia that states could not execute the mentally disabled because it violates the constitutional ban on cruel and unusual punishment. But it allowed states to develop their own criteria for mental disabilities.

Texas lawmakers, though, were unable to agree on criteria. Prosecutors wanted a standard in which jurors would decide during the penalty phase of a capital murder trial whether a defendant was too intellectually disabled to face execution, allowing them to consider the person’s past crimes in the decision-making. Defense lawyers supported creating a process that allowed a judge to evaluate the defendant’s mental fitness.

“A legislative fix is always preferable to a judicial fix when the parties can come together and agree on a solution,” Edmonds said. “The problem is that prosecutors and anti-death penalty advocates have never been able to agree on how to address this legislatively.”

In 2004, when Jose Garcia Briseño’s case came before the Texas Court of Criminal Appeals, the nine judges were without legislative guidance and developed their own standards. Lawyers for Briseño, who is still on death row, argued that he was mentally retarded and should not face execution for the 1991 murder of a Dimmit County sheriff’s deputy. The court rejected those arguments and in the process developed the so-called Briseño factors that are used now to determine whether Texas defendants are eligible for the death penalty.

The Texas Court of Criminal Appeals invoked, in part, an evaluation of Lennie from Steinbeck's book, writing that "most Texas citizens would agree that Steinbeck's Lennie should, by virtue of his lack of reasoning ability and adaptive skills, be exempt from execution. But does a consensus of Texas citizens agree that all persons who might legitimately qualify for assistance under the social services definition of mental retardation be exempt from an otherwise constitutional penalty?"

The court’s three-part definition requires the convicted inmate to have below average intellectual function, to lack adaptive behavior skills and to have had those problems prior to age 18.

Lawyers for at least 90 Texas death row inmates have brought so-called Atkins claims before the courts, arguing that their clients’ limited cognitive functioning exempted them from execution. Of those, 14 have been deemed mentally retarded and their sentences commuted to life in prison.

Prosecutors stopped asking legislators to approve standards after the court adopted the Briseño standards, Edmonds said, because they wearied of the fight with defense lawyers and because they were mostly satisfied with court’s solution.

“I think Texas can continue under the current standard and remain in compliance with Supreme Court case law,” Edmonds said.

But defense lawyers say that Texas still puts mentally retarded defendants to death, flouting the Supreme Court’s prohibition. They argue that Ellis’ bill is a critical step to ensure that the courts rely on scientific evaluations of mental capacity and that the state doesn’t violate the constitutional ban on cruel and unusual punishment.

“Reliance on the Briseño factors is frankly something that has made the state the butt of much scientific criticism,” said Kathryn Kase, director of the Texas Defender Service, which represents death row inmates.

Ellis’ bill would use the definition developed by the American Association on Intellectual Developmental Disabilities to determine whether a defendant is eligible for the death penalty. A key part of the standard set out in the proposal is that the defendant must have an IQ of 75 or below to be exempt from execution. Delaware, Idaho, Kentucky, Maryland, New Mexico, Nebraska, North Carolina, South Dakota, Tennessee and Washington use similar standards, but require an IQ of 70 or below for exemption.

“The most appropriate thing for state statute is to be parallel to existing definitions that are existing professionally within the field,” said Ed Polloway, dean of graduate studies at Virginia's Lynchburg College and a member of the AAIDD’s death penalty task force. The task force is developing a guide for states to use to evaluate defendants for intellectual disabilities.

“Our attempt is to stay as close to the science as possible,” Polloway said.

The AAIDD’s definition of intellectual disability, he said, is used to determine state and federal aid for programs like Medicaid and special education placement in schools. The existing Texas death penalty standard, Polloway said, would allow for the execution of individuals who are considered intellectually disabled for the purposes of government programs.

Ellis said basing decisions about who is fit for execution on established scientific research would save Texas money it would otherwise spend fighting inmates’ appeals.

“It will protect the rule of law and the integrity of our judicial system,” he said.