Complex sentence: A team from the Montreal Gazette investigated Fabrikant's academic credentials and discovered that he had emigrated from the USSR not as a political dissident, but because he had been fired from a succession of posts for his threatening and disruptive behaviour.
Split into simpler sentences: A team from the "Montreal Gazette" investigated Fabrikant's academic credentials and discovered that he had emigrated from the USSR not as a political dissident as he had claimed. Instead, he had been fired from a succession of posts for his threatening and disruptive behaviour.