Initially a dealer who focused on Judaica, antique books and manuscripts, Mr. Zarug said he began hunting for things to buy in the Soviet Union after the fall of the Berlin Wall. “The U.S.S.R. in 1990 was like the Wild West,” he said. Mr. Zarug said his diversification into Russian avant-garde art happened by chance. One of the dealers he had been working with regularly in Moscow offered him a painting attributed to Lissitzky for $3,000, he said, and back home in Israel, he displayed the painting for gallery owners in an exhibition in his office. The first person to arrive “didn’t even look at the Judaica, he just looked at the painting,” Mr. Zarug said. “I saw his interest and understood it was something of value, so I thought I would ask a very high price. I asked for $30,000. He said O.K.”

Mr. Zarug said he immediately returned to Moscow, bought another three paintings, and sold them to a dealer in Israel for a vast profit.

As he began searching for art in earnest across the Soviet Union, Mr. Zarug said he discovered huge stores of neglected paintings. On one occasion, he said, he found 100 pictures in very bad condition covered with a dust sheet in an attic in Moscow and bought them for $1,000 each. On another, he said, he was taken to a deserted building in Azerbaijan where he was offered 206 paintings — including works he said are by Malevich and Kandinsky. In Tajikistan, the staff members of a museum sold him artworks directly from the basement, he said.

Some of Mr. Zarug’s acquisitions were more orthodox. He said he traced Chagall’s family in St. Petersburg and purchased some works on paper from Oxana Kornienko, the granddaughter of Chagall’s sister Lea, as well as an oil self-portrait dating from 1917 that has since been authenticated by the Comité Chagall in Paris and sold to a private collector. The Comité said it could not comment on whether Mr. Zarug had been the person who had the painting authenticated.

Some works he sold out of a gallery he had in Wiesbaden. The rest, he said, he kept in the private collection that was seized by the police. The authorities confiscated some 1,800 works, most of which are being returned to him.

Though he was convicted on the lesser counts, and sentenced to 32 months in jail, he had already been incarcerated for that length of time while he awaited trial, so now he is free. Mr. Hazaz, his partner, who was sentenced to three years, has also served his time.