Complex sentence: Marry left a newborn son David Kobakhidze with the neighbor when she was taken away for questioning, before being executed she had a chance to write a letter to him that is the only possession David had left of his mother.
Split into simpler sentences: Marry left a newborn son, David Kobakhidze, with the neighbor when she was taken away for questioning. Before being executed she had a chance to write a letter to him that was the only object he had from his mother.