According to the story Zborowski told friends, his conservative parents moved to Poland in 1921 to escape the October Revolution in Russia.

In 1933, the penniless Zborowski turned up in Paris with his wife and was recruited as an NKVD agent by the Leningrad émigré Alexander Adler.

Suddenly he became violently ill, and despite repeated blood transfusions, he died in great pain on 16 February at the age of thirty-one.

Etienne now became the leader of the beheaded Trotskyist organization in Paris and continued to edit the Bulletin of the Opposition, along with Lilia Estrin Dallin (codename NEIGHBOR).

He used his skills to play upon the vanities of the remaining Trotskyists and create internal divisions within the faction, especially isolating Victor Serge.

In 1939, the defector Alexander Orlov sent Trotsky an unsigned letter warning him that an NKVD agent named "Mark", fitting the description of Zborowski, had infiltrated the Paris organization.

Much to her later regret, Dallin convinced Trotsky that the letter was NKVD disinformation meant to create fear within the Trotskyist faction.

At the founding conference of the Fourth International in Paris in September 1938, Etienne introduced his friend Sylvia Ageloff, an American Trotskyist and interpreter, and probably the Soviet agent, to Ramón Mercader, the future assassin of Trotsky.

The American Trotskyists David and Lilia Dallin assisted in his emigration and helped him obtain employment at a screw factory in Brooklyn.

With money from an unknown source, he rented a fashionable Manhattan apartment in the Dallins' building and once again resumed his former occupation, spying on Trotskyists.

Zborowski spied on the Dallins and helped the NKVD search for Victor Kravchenko, a Soviet engineer and mid-level bureaucrat who defected from a trade mission in 1944.

Kravchenko published a book, I Chose Freedom (1946), which described the repressions in the Soviet Union, the purges, the collectivizations, and the slave labour camps.

He turned his attention to his academic career and found employment, with the aid of Margaret Mead, as a research assistant at Harvard University.

In his testimony he claimed that the NKVD had tried to enlist him as an agent in New York but he had refused: "At that time, I became almost--I became hysterical and I remember well, I hit my fist on the table and said, 'I will not do anything with you anymore.'

When they were both living in the United States, Zborowski twice visited the home of Elisabeth Poretsky one day in the spring of 1955, she believed according to her memoirs.

He did not wait for me to ask him anything, however, but began to tell me how he had been recruited by a fellow worker, a Russian, in Grenoble, who had suggested he go to Paris, where he could find friends and "be useful to the Soviet Union."

But amidst the huge body of material about Jews collected for Mead's project... is an interview with Zborowski about his childhood and youth that is probably the most honest statement he ever recorded.

He provided the information in 1947, just before anti-communism surfaced as a major post-war preoccupation, two years after his espionage work had ended, and almost a decade before he was unmasked.