Mafia’s ties to the movie industry. He went on to prosecute several organized crime figures who had infiltrated the International Alliance of Theatrical and Stage Employees and extorted huge sums of money from Hollywood studios and neighborhood cinemas. That 1943 case was among the first to lead to convictions for murder, extortion and conspiracy directly under federal statutes, not state laws.

Soon afterward, Mr. Kostelanetz was appointed chief of the war frauds section of the Justice Department, which examined fiscal irregularities during World War II. From 1951 to 1952, he served as special counsel to a United States Senate committee headed by Estes Kefauver. The televised hearings of the committee showed the extent to which Mafia figures had received special treatment from government officials.

Yet Mr. Kostelanetz always said he felt more at home as a courtroom advocate than an administrator on Capitol Hill. In 1946, he helped found the law firm that evolved into Kostelanetz & Fink, and he continued to show up at the office regularly until just before he died.

During his long career, Mr. Kostelanetz handled a heavy load of tax evasion cases. Among the clients he defended were Bobby Baker, a protégé of President Lyndon B. Johnson; Dr. W. Kenneth Riland, the physician to President Richard M. Nixon and Gov. Nelson A. Rockefeller; and Anthony Conrad, chairman of the RCA Corporation. His efforts were frequently successful.

Born in 1911 to a wealthy family in pre-revolution Russia, Mr. Kostelanetz and his family fled St. Petersburg and eventually arrived in New York when he was 9. His brother Andre went on to become a world-famous conductor.

In 1933, Mr. Kostelanetz joined Price Waterhouse as an accountant. But to stand out from his peers, he enrolled at St. John’s University law school at night. Upon graduating from law school, he joined the United States attorney’s office in New York, where his financial background made him the expert in prosecuting complex securities and tax crimes.

Mr. Kostelanetz was an adjunct professor of taxation at New York University, where he also served as a trustee. He was also president of the New York County Lawyer’s Association and chairman of the character and fitness committee of the Appellate Division, which oversees the admission of lawyers to the bar.