The Oct. 3 execution of Terrence Williams, 46, was halted indefinitely by a judge who cited the suppression of evidence and prosecutor misconduct in the case, which stemmed from the 1984 beating death of Amos Norwood, 56, of Mount Airy.
District Attorney Seth Williams said his office would file an appeal with the Pennsylvania Supreme Court to have the death sentence reinstated.
"The well-deserved death sentence imposed by a jury on a vicious ... murderer has been unjustly overturned by a Philadelphia judge, 28 years after the crime," Williams told reporters.
Friday's ruling by Common Pleas Judge M. Teresa Sarmina did not affect the death row inmate's conviction. It will, however, require a new penalty hearing during which his sentence could be changed to life in prison, the Philadelphia Daily News reported.
Sarmina read a 15-minute statement during Friday's hearing accusing prosecutors of "gamesmanship" and failure to turn over evidence that Williams had been sexually molested by the victim.
"Ultimately, the non-disclosure of that evidence undermines confidence in the jury's death sentence," Sarmina said.
Seth Williams defended the actions of then-prosecutor Andrea Foulkes, who is now a federal prosecutor, and said she had been "victimized" by Sarmina.
Senate Democrats to pull all-nighter on climate change
Interpol investigating stolen passports on missing flight