MIAMI (AP) — A federal judge on Saturday granted a stay of execution for a convicted mass killer in Florida, who is mentally ill and was scheduled to be put to death on Tuesday.

U.S. District Judge Daniel T. K. Hurley granted the motion for a stay in the case of John Errol Ferguson, who was to be executed Tuesday after 34 years on Florida’s death row.

“The issues raised merit full, reflective consideration,” the court said.

The court will hear three hours of arguments on Ferguson’s habeas corpus petition on Friday, according to his attorneys.

They contend that the Florida Supreme Court, in determining that Ferguson could be executed, relied on an outdated definition of competency that conflicts with a 2007 U.S. Supreme Court ruling. Ferguson’s attorneys maintain he is insane and that the Constitution prohibits the state from executing him.

“In order for the state to execute him, Mr. Ferguson must have a rational understanding of the reason for, and effect of, his execution,” said Chris Handman, an attorney for Ferguson, in an emailed statement. “A man who thinks he is the immortal Prince of God and who believes he is incarcerated because of a Communist plot quite clearly has no rational understanding of the effect of his looming execution and the reason for it.”

Attorneys for the state could not immediately be reached for comment Saturday evening.

The 64-year-old Ferguson was convicted of killing eight people including six who died execution-style in 1977 in Carol City, which at the time was the worst mass slaying in Miami-Dade County history. He also was convicted of killing a teenage couple from Hialeah in 1978.

Two accomplices in the drug-related Carol City killings, Beauford White and Marvin Francois, also were convicted of murder. Both were executed in the 1980s.

The state Supreme Court this month upheld a lower court ruling based on testimony by a panel of psychiatrists appointed by Gov. Rick Scott that Ferguson is legally competent to be executed even though he suffers from paranoid schizophrenia.

The state justices wrote that “Ferguson understands what is taking place and why.”

Ferguson’s lawyers contend an inmate’s awareness of his execution as the state’s rationale for putting him to death is not enough.

They argue the inmate must have a “rational understanding,” a higher standard than mere awareness. The U.S. Supreme Court set the rational understanding standard in a 2007 case, but the Florida justices noted that the opinion specified that it wasn’t attempting to “set down a rule governing all competency determinations.”

Ferguson lacks rational understanding, his lawyers say, because he suffers from delusions that he’s the “prince of God” and that God is preparing him to return to earth after his execution and save the United States from a communist plot.

Attorneys for Ferguson had previously challenged the procedure that Scott used to deny Ferguson’s clemency request, but the U.S. Supreme Court declined to hear that appeal and rejected a stay, 7-1. Justice Stephen Breyer would have granted the stay. Chief Justice John Roberts did not participate. Ferguson’s attorneys then filed the new appeal.