Texas plans to execute Scott Panetti, a mentally ill man convicted of murder, on Wednesday. Supporters are trying to convince Gov. Rick Perry to change Panetti's sentence to life in prison. Reuters

Activists have urged Texas Gov. Rick Perry to stay the execution of a mentally ill man scheduled for Wednesday. The case of Scott Panetti, a schizophrenic 56-year-old who fatally shot his wife's parents in 1992, has sparked discussion about the state's death penalty laws and the definition of competency. Panetti's lawyers argue the execution is unconstitutional due to the Eighth Amendment's prohibition on cruel and unusual punishment, but prosecutors say Panetti has exaggerated his mental illness.

Panetti was convicted in 1995 for the double murder of his in-laws. At trial, he represented himself, wore a cowboy costume and tried to subpoena the Pope. Panetti pretended to shoot the jury, testified about castrating his horse and said his alter-ego "Sarge," not him, killed the victims.

His execution is in the spotlight because the U.S. Supreme Court outlawed executions of people who cannot understand why they're being put to death in 1986. But it didn't explicitly define mental competency, which lawyers argue Panetti lacks. He suffers from schizophrenia, paranoia and delusions. He's been hospitalized for mental illness 15 times since 1978, and he sees his life as a spiritual war against Satan.

Panetti was last tested for competency in 2007, BuzzFeed reported, and his lawyers say his mental state has continued to decline. "He is hearing voices, believes that a listening device has been implanted in his tooth and that the State wants him to ‘shut up’ about corruption on death row and stop him from preaching the Gospel," said his lawyer Kathryn Kase in a statement."Mr. Panetti’s serious mental illness has infected every stage of his case. He is not the worst of the worst for whom the death penalty is intended."

But many witnesses told the court that Panetti actually does grasp that he's being punished for the murders. The state of Texas produced recordings of Panetti talking about the crimes. TIME reported that court documents showed Panetti "spoke rationally, demonstrated a fairly sophisticated understanding of his case, and discussed in an intelligent manner the death penalty and its moral implications."

In efforts to stop the execution, his lawyers filed appeals with Texas' district court and court of criminal appeals. Both were denied this week. Separate appeals with the U.S. Supreme Court and 5th Circuit Court of Appeals are pending.

Meanwhile, nearly 97,000 people have signed a change.org petition on Panetti's behalf. USA Today reported his public supporters include the American Psychiatric Association and the American Bar Association, as well as former Texas Gov. Mark White and former congressman Ron Paul. The latter two were among 21 conservative politicians who requested Perry change Panetti's death sentence to life in prison. "As conservatives, we must be on guard that such an extraordinary government sanction not be used against a person who is mentally incapable of rational thought," they wrote in a letter.

Texas executes more people than any other state in the U.S. About 280 inmates have received the death penalty under Perry.