Complex sentence: Since 1912 he was placed under Imperial protection, but in January 1915 Stepan Petrovich Beletsky, head of the police, exercised 24-hour surveillance of him and his apartment.
Split into simpler sentences: Since 1912 he was placed under Imperial protection. In January 1915 Stepan Petrovich Beletsky, head of the police, exercised 24-hour surveillance of him and his apartment.