(CNN) -- The attorney for a Florida man convicted of killing eight people asked the U.S. Supreme Court Tuesday for an emergency stay of execution, he told CNN.
John Ferguson, a diagnosed schizophrenic, is on death row for the murders in Hialeah and Carol City, Florida, in the late 1970s.
He was scheduled to be executed Tuesday at 6 p.m. ET at the Florida State Prison.
The Supreme Court "has said it's a 'miserable spectacle' to execute the insane," Chris Handman, the Washington D.C.-based attorney for Ferguson, told CNN. "We think the court should intervene to stop that execution from going forward today."
Handman said a court found that Ferguson was mentally ill and had delusions which caused him to think he is the "Prince of God." A stay had been granted by a federal district court because of concerns about his mental capacities but that ruling was reversed by an appeals court.
"We think there are substantial constitutional questions here that will merit the Supreme Court of the United States to honor the stay of execution," Handman said. "We hope to hear from the Supreme Court in the next few hours."
In the meantime, officials at the prison in Starke, Florida, will go ahead with preparations for the execution, including fixing Ferguson's last meal, Misty Cash with the Florida Department of Corrections told CNN.