For an old soldier who had spent a life on the run, it wasn't much of a jump. After sneaking down from his third-floor hotel room to a second-floor terrace, former SS Major Karl Hass tied his gray jacket around a balcony railing and lowered himself toward the ground. Forced to leap the final 3 m, he landed on a row of flowerpots and fractured his hip. Bones are brittle at age 84.

"He's crazy! He's crazy!" exclaimed Erich Priebke upon learning of his old comrade's escapade. But Priebke, 82, a former SS captain on trial in Rome for the 1944 massacre of 335 civilians, knows well the demons that can pursue a cornered ex-Nazi. "In all these years, this issue has been like a weight in my heart," he reportedly told prosecutors after his capture in Argentina last year and subsequent extradition to Italy. He has been on trial since May 8 on charges of participating in a massacre with premeditation and cruelty, and faces a possible life sentence or permanent house arrest.

Long thought to be dead, Hass was tracked down to his daughter's house in Geneva. He agreed to testify at Priebke's trial on condition that he would be allowed to return home afterward. As a German- embassy staff member in Rome during the Nazi occupation, Hass was in a position to know exactly what happened during the night of March 24, 1944, when Priebke's SS unit rounded up those hostages and machine-gunned them in the Ardeatine caves near the Christian catacombs on the outskirts of Rome. The executions were a reprisal for the killing two days earlier of 33 German soldiers by Italian resistance fighters.

Priebke admits to having personally executed two prisoners; witnesses allege he also tortured several of them. His defense rests mainly on the standard war criminal's claim to have been acting on orders from above. It was ex-SS Colonel Herbert Kappler, said Priebke, who decreed the killing of 10 Italians for each dead soldier and warned that any German officer refusing to carry out the mass execution would be shot. Kappler died in 1978, one year after he escaped from a military hospital while serving a life term for his role in the massacre.

But Kappler's ghost continues to haunt the case. Two weeks ago, Italian radio discovered a 22-year-old tape of a recorded newspaper interview in which the late SS colonel had said that Priebke could have chosen not to take part in the killings. Having a live witness confirm that claim in court would have substantially weakened Priebke's defense. Hence the prosecution's eagerness to hear from Hass, especially after he gave several newspaper interviews suggesting that Priebke could have disobeyed Kappler's orders. Hass, alias "the Fox," had also told Italian reporters that Priebke was behind the capture of the King of Italy's daughter, Mafalda di Savoia, who later died at Buchenwald.

But by the time he arrived in Rome on June 6, the star prosecution witness appeared to be getting cold feet. After five hours of preliminary interrogation by military prosecutor Antonino Intelisano, Hass retired at 8 p.m. to the Hotel Gerber, whose doors were heavily guarded by police. At about 5 a.m., the Fox tried to fly the coop. A younger and nimbler man would probably have made a clean getaway. But Hass, writhing in pain, was immediately rushed to Rome's Celio military hospital.

What had compelled an old man to attempt such desperate acrobatics? He told Intelisano that stress--"a rush of blood to the head"--had prompted him to flee rather than testify against a fellow ex-Nazi. Some investigators speculate that he may have been spooked by a late-night phone call, perhaps a threat from the notorious underground Odessa network that in the past helped Nazis escape justice.

In any event, Hass was singing a very different song last week when prosecutors took his deposition in the hospital library. Instead of fingering Priebke, he defended the accused, saying the reprisal order ultimately came from Hitler and could not have been disobeyed. Instead of denying his own responsibility, as he had in his press interviews, Hass admitted that he too had killed two people. "I don't remember who organized the whole thing," he said. "I only know that Priebke had the list [of hostages] in his hand and checked it" as each victim was taken off the trucks and led off to be executed. Explaining the discrepancy between the 330 reprisal killings that had been ordered and the 335 bodies found in the caves, Hass said the extra five were additional hostages who had been rounded up.

But Hass's two hours of bedside testimony contained numerous contradictions. Undermining the kill-or-be-killed claim, he noted that two SS officers who fainted on the scene of the executions did not have to participate. He added that Kappler could have rejected the orders but decided to carry out the killings "so he could show off" at a meeting in Berlin.

It remains to be seen whether Hass's high-wire antics and selective memory have fatally undermined his credibility as a prosecution witness, which may have been his aim all along. Priebke had called him crazy, but he may be crazy like a fox.

--Reported by Toula Vlahou/Rome