After reading the appeal from prison inmate Mark Spotz, incarcerated on four murder convictions, an angry Chief Justice Ronald D. Castille unleashed perhaps the most scathing language ever from the Pennsylvania State Supreme Court.

His target was not the killer; it was the highly specialized Capital Habeas Unit, 35 mostly federally funded defense lawyers who handle death-case appeals and whom Castille accused of legal "sabotage."

Spotz's cases have been in court for more than a decade. He was convicted in 1996 of four murders in four counties over three days. In three of the four trials, he was sentenced to death. Castille had before him a 100-page brief filed by four habeas unit lawyers and crammed with 70 claims. It appealed just one of Spotz's convictions.

So no matter the outcome, Spotz would remain in jail on his other death sentences.

To Castille, the massive legal document, and the government-funded work it represented, "bordered on the perverse."

It was an example, he wrote last month, of federal defense attorneys using an intentionally "abusive" strategy intended "exhaust as much of this court's time and resources as possible" and frustrate the legitimate exercise of the death penalty.

He called it, "The zealous pursuit of what is difficult to view as anything but a political cause: to impede and sabotage the death penalty in Pennsylvania."

On Friday, the federal defenders responded with their own lengthy written blast, calling the former Philadelphia district attorney's accusations "unwarranted" and "unfounded." They also denied a "suggestion" from Castille that using federal lawyers in state courts was a misuse of federal money.

Behind the unusual dispute is the fact that, although the death penalty is on the books, it is not used in Pennsylvania. There are 215 people on death row in the state, but no one has been involuntarily executed in about three decades. The last execution was in 1999, when torture-murderer Gary Heidnik voluntarily halted his appeals.

Long-running litigation in death-penalty cases has long angered prosecutors and some victims' relatives - particularly the spouses of police officers killed on duty - even as law enforcement officials concede there is a need for review. Most of the cases on appeal are more than a decade old, as Pennsylvania juries have become more reluctant to impose death in first-degree murder cases.

The federal defenders say they are merely doing what they are paid to do: provide the best representation possible. They cannot choose who deserves the best effort, said Leigh M. Skipper, the chief federal defender based in Philadelphia. "We take the cases as we find them. We can't differentiate between 'good murderers' and 'bad murderers.' A lawyer has an ethical obligation."

The lawyers also sharply rejected Castille's complaints that they nitpick to deliberately clog the court.

"As a lawyer who is appointed to represent someone, we don't have the luxury of saying, 'Well, it's close; we don't make this argument,' " said David Rudovsky, president of the Defender Association of Philadelphia, which oversees public defenders in state and federal courts. "Frivolous claims are in the eye of the beholder," he said.

In the last 15 years, the defenders have represented 14 inmates whose convictions or death sentences were overturned by the State Supreme Court, and 19 whose death sentences or convictions were vacated by a federal court.

One of those was Zachary Wilson, a Philadelphian convicted of murder in a 1988 killing and sentenced to death. In 1995, the state Supreme Court overturned the verdict and the sentence. In 2009, both were vacated and a new trial was ordered by the U.S. Court of Appeals for the Third Circuit, which observed that at Wilson's original trial there was no physical evidence, and that exculpatory evidence involving the three chief state witnesses was withheld from the defense.

Never disclosed was that one of the witnesses had a lengthy history of schizophrenia and was hospitalized the day after testifying; another had three convictions for impersonating a police officer and suffered from brain injuries that impaired his memory; and the third had a history of receiving interest-free loans from a police sergeant.

"We have no doubt that . . . trial counsel . . . would have used all this information to impeach the commonwealth's witnesses," the judges wrote.

But the defenders say they are not right every time.

"What is not proper is the way this litigation is conducted," said Cumberland County District Attorney David J. Freed, whose office is prosecuting Spotz, whom he called evil.

"There is no other word to describe him. And he is guilty beyond any doubt."

The habeas unit - the word comes from "habeas corpus," the legal term for a mandatory court appearance to prevent illegal confinement - spends about $14 million a year representing death-row inmates. That is equivalent to half the annual budget of the Philadelphia District Attorney's Office.

The District Attorney's Office handles 70,000 cases a year; the habeas unit, with about 35 staff lawyers assisted by outside lawyers working pro bono, has 40 to 50 active appellate cases statewide, said Ronald Eisenberg, the deputy district attorney who oversees appellate cases.

In state court on Friday, Eisenberg said, one assistant district attorney handling a murder appeal was facing six attorneys.

"We have one expert, they have five," Eisenberg said.

That disparity annoys prosecutors, and Castille asked for state and federal legislators to look into how the federal money is spent.

Federal money is typically not supposed to be used to pay for attorneys in state court, all sides agree.

For years, the defenders have refused to say how they pay for such extensive work in state court, Eisenberg said.

A 2001 letter from federal officials said it was with "grants and donations," Eisenberg said.

Rudovsky said federal money paid for most of the work and that federal statutes allowed it.

When cases are still in state court on appellate review, the federally paid lawyers can help research and prepare cases, he said, because "they would get that case when it goes to federal court." They cannot appear in court.

Particularly in appellate cases, pretrial work can be far more time-consuming and expensive than court appearances.

And when federal judges order a case back to state courts for a rehearing, habeas unit lawyers are allowed to handle the entire case, Rudovsky said.

"A lot of the time we spend in state court is chargeable to the federal representation," he said.

The office also has about $130,000 in private money it uses for some state work. About $100,000 comes from a foundation established by George Soros, the billionaire financier, to "assure greater fairness in political, legal, and economic systems," its website says.