The judge granted a stay of execution Tuesday after Middleton's mental capacity was called into question.
Middleton was scheduled to be put to death at one minute past midnight but his lawyers argued he is not mentally competent to be executed.
The judge wants to hold a hearing to determine if Middleton is insane.
Middleton, who was convicted of dealing methamphetamine, has been on death row since 1997 for the murder of another drug dealer in Harrison County near Ridgeway in 1995.
He was also convicted of killing two other people in Mercer County.
Authorities say the killings were an attempt to cover up an illegal meth operation.
Middleton would be the sixth execution carried out in Missouri this year.
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