Sonnenfeldt died Friday at his home in Port Washington on Long Island, said his wife, Barbara. The cause of his death was complications of a stroke, she said Tuesday.
Sonnenfeldt interrogated some of World War II's most notorious Nazi leaders, including Hitler's second-in-command, Hermann Goering; Albert Speer, who headed Germany's war manufacturing; and Reich minister Rudolf Hess. They were all convicted as war criminals.
A German-born Jew, Sonnenfeldt was a U.S. Army private who helped liberate the Dachau concentration camp when he was selected as interpreter because of his bilingual skills.
He recounted that role in his memoir, "Witness to Nuremberg."
"He was a very remarkable man, a very talented, multifaceted guy. He was also a humanitarian," his wife said.
Sonnenfeldt later graduated from Johns Hopkins University with a degree in electrical engineering and went to work for RCA, where he helped develop color television. In the 1980s, he was dean of the Graduate School of Management at the Brooklyn Polytechnic Institute.
An avid sailor, Sonnenfeldt crossed the Atlantic three times in his 70s.
Sonnenfeldt is survived by his wife; sons, Michael and Lawrence, and daughter Ann Goldberg; three stepchildren, Elizabeth Holdstein, Catherine Hausman and Maggi DeNicola; and his brother, Helmut, who was National Security Council adviser in the Nixon administration.
His first wife, Shirley, died in 1979.
Sonnenfeldt was buried in Pinelawn Cemetery in Melville, N.Y.