The Florida Supreme Court on Wednesday upheld a judge’s decision finding Miami mass murderer John Errol Ferguson sane to be executed.

Justices said there was “competent, substantial evidence” to support Bradford Circuit Judge David Glant’s ruling that Ferguson understands why he is to be executed — for eight Miami-Dade murders in the late 1970s.

Ferguson, 64, had originally been scheduled to die by lethal injection this week at the Florida State Prison in Bradford. A new date and time must now be set.

Defense attorneys have maintained for decades that Ferguson is severely mentally ill and his execution would be “cruel and unusual punishment.”

On Wednesday, lawyer Christopher Handman said he was “disappointed” by the decision. He plans to appeal to the U.S. Supreme Court.

“No justice will be served by executing a very sick, elderly man,” Handman said.

In his order, Glant acknowledged that Ferguson has a history of schizophrenia but that he exists now trouble free in prison and “there is no evidence that he does not understand” why he is to be executed.

The judge also noted that while Ferguson claims he is the “Prince of God” and will be seated at the “right-hand” of God after his death, his beliefs are not “significantly different than beliefs other Christians may hold,” Glant wrote.

Ferguson’s defense attorneys have criticized the court’s ruling. They filed an appeal with the Supreme Court, including testimony from two university professors who say Ferguson’s religious beliefs are not “normal.”

Ferguson was convicted of the July 1977 murders of six Carol City residents during a home-invasion robbery. At the time, it was the worst mass murder in Miami-Dade history.

Ferguson, now 64, also was convicted separately of murdering two teenagers, Belinda Worley, a 17-year-old Hialeah High School senior, and Brian Glenfeldt, 17, in January 1978.

The two teens had gone out for ice cream, and Ferguson pretended to be a police officer when he stopped them. He shot Glenfeldt to death and raped and murdered Worley, and stole her class ring.