Slagle has been on death row since 1988. He served his time at the Chillicothe Correctional Institution where he was found dead in his cell just after 5 a.m. Sunday said Jo Ellen Smith, a spokeswoman for the state Department of Rehabilitation and Corrections. He was due to receive a lethal injection Tuesday.
Slagle was convicted for murder after stabbing a neighbor to death in her Cleveland home. He petitioned for clemency on July of this year but his request was denied by Gov. John Kasich on July 24 after a board voted 6-4 on the issue.
The refusal came in spite of the support of Cuyahoga County Prosecutor Timothy McGinty, who recommended Slagle's sentence be reduced to life in prison without parole.
McGinty claimed that even though there was "no doubt of Slagle's guilt," at the time of his conviction it was not a option for the jury to convict him to life without parole. He added that if the case had taken place in present day, prosecutors wouldn't have sought the death penalty.
Slagle was 18 years old and had a prior record when he was arrested for the murder of Mari Anne Pope, who was stabbed 17 times with scissors while her children were in the home, according to court records.
Prison officials have launched an investigation into how Slagle died. He was in solitary confinement at the time of the incident. An autopsy was scheduled for Monday, said chief investigator for the Ross County Coroner's Office, Mike Ratliff.