Complex sentence: Identified by a double agent (1) who was placed in the cell when he was arrested, he managed to earn their trust; he was arrested in Nice on 4 January 1944 with Captain Dupouy, his deputy.
Split into simpler sentences: Identified by a double agent who was placed in the cell when he was arrested, he managed to earn their trust. He was arrested in Nice on 4 January 1944 with Captain Dupouy, his deputy.