Perhaps the most celebrated Nazi war criminal still at large is Dr. Josef Mengele, who was described by the little Jewish girl Anne Frank as "the angel of extermination" at Auschwitz concentration camp. With a wave of his cane, he decided which Jews should go to the gas chambers, which should be used for medical experiments, which should be worked to death.

Trusted sources say the tall, gray-haired Mengele is hiding somewhere in the rain forests of Paraguay. He reportedly keeps on the move, frequently changing his home base; sometimes he travels abroad on false passports. Both passports and protection are provided by Paraguay's dictator, Alfredo Stroessner.

Over the years, I have tried to catch up with Mengele. I came close in 1960. I located some of his closest associates in Buenos Aires, where he once operated a small chemical plant. They boasted that he hadn't bothered to change his name at first - a gesture they regarded as evidence of his "courage."

But by 1960, he was on the run under many names, and he eluded me. Insetad, I uncovered another mass murder, Herbet Cukurs. They were linked, it turned out, to the select circle of mass killers. Insiders say my report on Cukurs therefore forced Mengele's hand. It is a bizarre story whose publication might yet help to flush out Mengele.

I learned from a former Nazi SS officer that Cukurs operated a seaplane service that gave joyrides to vacationers in Brazil. Sometimes he flew other Nazis-on-the-run into the interior.

Cukurs had taken a leading part in the massacre of 32,000 Latvian Jews in 1941. Eyewitnesses described Cukurs as strutting about in a black leather coat, brandishing a pistol, as Jews were brutalized and murdered. He barricaded some Jewish worshippers in their synagogues and burned them alive.

I followed the directions of the SS officer and found Cukurs holed up in a white-and-blue lakeside bungalow not far from Sao Paulo. Two bodyguards took my White House press card to him and mentioned the name of the SS officer who had sent me.

Cukurs waved me in. He was wearing a black leather jacket, and the barrel of a pistol protruded from his hip pocket. In my career as a reporter, I have seen frigtened men, but no man so deathly afraid as Herbert Cukurs. All the old Nazi bluster had drained from his stocky figure.

"I don't have the blood of any Jews on my hands," he pleaded. "I was not a leader of the Nazi Party in Lativa. I was a simple mechanic. All I did was to repair the party's trucks. I was too busy for politics and Jew killing."

Once he went to the closet to get some documents. Through the closet door, I saw several Nazi uniforms, cleaned and pressed, hanging in a row. They were impressive uniforms for a truck mechanic.

Afterward, I wrote a story about Cukurs that disclosed his whereabouts. The story told how the hunters had become the hunted, how they were pursued by shadows, how the next shadow could be that of an executioner.

THis was not the last story to be written about him. A few years later, the wire services carried another story. His body, stuffed in a trunk, had been found in an abandoned house in Montivideo, Uruguay. There was only one clue to the identity of his killers. A note pinned to his jacket said: "The Committee That Never Forgets."

It appeared that the Latvian Jews had finally been avenged. But my sources tell a strangely different story. They say that Cukurs tried to make a deal with the Jewish underground after I published his whereabouts. In return for his safety, plus $100,000 in cash, he offered to lead them to Mengele. Although both Cukurs and Mengele, in absentia , had been named war criminals at Nuremberg, Mengele clearly was the bigger catch.

Cukurs informed the Jewish agents that Mengele was hiding out in paraguay across the Parana River form the small Argentina town of El Dorado. He lived in comfort and owned a boat called Viking 11, Cukurs said. He warned that it would be impossible to approach the Mengele hideout by road without being spotted. He also said the nearest Paraguayan town was a haven for ex-Nazis, who were armed and dangerous.

Cukurs offered, upon payment of the $100,000, to fly the Jewish commandos into the area by seaplane. They coudl land secretly on the Parana River and approach Mengele by water.

My sources say that Mengele got wind of Cukurs' doublecross. Not long afterward, two men showed up in Uruguay on a Lufthansa airliner from Dusseldorf. They carried phony passports identifying them as Heinz Oswals Taussig and Anton Kunzle.

A girl at the Lufthansa ticket office remembered them. She was also able to identify a picture of the muscular Cukurs who, she said, had once accompanied them to the ticket office. She remembered that Cukurs had used the familiar German term "du" in talking to them, indicating they were friends.

My sources suggest that Cukurs was murdered by two men he believed to be friends. His skull was crushed by blows from a hammer. The murder room showed signs, too, of a struggle, including three bullet holes. The bullets, fired wildly, had come from the pistol Cukurs always carried.

Despite the pains to make the murder like a Jewish plot, the two assassins were not Jewish. My sources believe he was slain by the Nazi underground, although he had been one of its heroes.

Did Mengele, learning of Cukurs' offer to sell him out, order his assassination? Is Mengele still able to condemn men to death with a flick of his cane? Does the Nazi underground, sometimes called the "Spider" by Nazi romantics, still take orders from the old dealers in death? My sources believe so.