Investigators of the Russian plane crash in Egypt are '90 percent sure' the noise heard in the final second of a cockpit recording was an explosion caused by a bomb, a member of the investigation team told Reuters on Sunday.
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Reuters: Investigators ’90 percent sure’ bomb downed Russian flight in Egypt

A handout picture taken in Cairo on November 2, 2015, and released on November 3, 2015 by the Egyptian civil aviation ministry shows one of the two black boxes of the Airbus A321 Russian airliner, that crashed in Sinai Peninsula killing all 224 people on board.