Complex sentence: Ossowieki was taken into custody during mass arrests sparked by the uprising in August 1944, and was among an estimated 10,000 people machine-gunned to death in a Warsaw park, less than six months before the Soviet Red Army entered the city.
Split into simpler sentences: Ossowieki was taken into custody during mass arrests sparked by the uprising in August 1944. He was among an estimated 10,000 people machine-gunned to death in a Warsaw park, less than six months before the Soviet Red Army entered the city.