Complex sentence: According to FBI files he had been emprisoned in Estonia in 1898 and in an interview in the New York Times he had been involved in revolutionary activity in Kronstadt during the 1905 revolution.
Split into simpler sentences: According to FBI files he had been emprisoned in Estonia in 1898. In an interview in the New York Times he said he had been involved in revolutionary activity in Kronstadt during the 1905 revolution.