Cathie Abookire, a spokeswoman for District Attorney Lynne M. Abraham, said: "We disagree with the judge's decision, and we will appeal."
Peterkin's court-appointed death-penalty lawyers could not be reached for comment yesterday.
Peterkin, 51, housed at the Greene state prison near Pittsburgh, will remain in custody pending appeal or retrial.
Peterkin was convicted in the Nov. 29, 1981, robbery and murders at the Sunoco station at Broad and Catharine Streets in South Philadelphia.
The killings were discovered when a friend of Ronald Presbery, 25, a gas-station attendant, went to the station about 6:30 p.m. and found him shot to death in a locked cashier's booth.
The body of manager John Smith, 59, was found in a locked boiler room at the station. Police said the shooter used two revolvers, a .32-caliber and a .38, on both men. Presbery was shot 15 times and Smith nine times. The shooter had to reload five times, police said.
Peterkin, of the city's Fern Rock section, had worked at the service station for about six weeks before being fired two months before the killings. He surrendered to police Dec. 2, 1981, after learning that an arrest warrant had been issued for him.
Peterkin was convicted nine months later and received two death sentences from Common Pleas Court Judge Albert Sabo for the killings and 12 1/2 to 25 years in prison for the robbery, in which $4,200 was taken.
In 1983, shortly after beginning his term on death row - then at the Graterford state prison in Montgomery County - Peterkin joined two other inmates in a hunger strike protesting the restrictions on condemned prisoners, who were then housed in solitary confinement and had no direct access to the prison's law library.
Later that year, Peterkin filed a federal class-action lawsuit over death-row conditions in state prisons. The suit resulted in federal-court hearings at Graterford at which Peterkin and other condemned inmates testified, but the suit was dismissed in 1987.
Joyner's decision came in the third of three possible appeal phases of Peterkin's conviction and death sentence, a federal proceeding known as habeas corpus. Peterkin's direct appeal has been rejected by the U.S. Supreme Court. A second appeal under the Pennsylvania Post-Conviction Relief Act was denied by the state Supreme Court in 1994. The habeas petition raised 15 purported violations of Peterkin's rights under the Constitution.
Among the issues on which Joyner based his ruling granting Peterkin a new trial:
Sabo's allowance of hearsay testimony by two men who said they pulled up to the gas island and claimed Presbery walked to their car and told them that Peterkin was in the cashier's booth with a gun and the dial to the cash safe. Joyner noted discrepancies in the testimony of one of the men and said there was no evidence to corroborate the reliability of the pair's testimony and make it admissible under one of 20 exceptions to the rule barring hearsay testimony.
Assistant District Attorney Roger King improperly inflamed and prejudiced the jury against Peterkin in his closing arguments by saying Peterkin had also committed welfare fraud.
King improperly argued to the jury that Peterkin was trying to deceive them by invoking his Fifth Amendment right and not testifying in his own defense at trial.
The prosecutor improperly suggested to the jury in arguing for the death penalty how the two victims might have testified and what they might have felt, and told the jury that "mercy has no part in your deliberation."
Lawyer Vincent Lorusso provided an "ineffective defense" by failing to investigate or present an purported alibi witness for Peterkin and by failing to present any character or background witnesses during the penalty phase of the trial.
Joseph A. Slobodzian's e-mail address is firstname.lastname@example.org.