Complex sentence: On the day of the November executions, machine guns began firing at the prisoners, they were used to clear the cells full of prisoners, of the survivors there were three people who escaped and shared their memory of what happened that day in the prison.
Split into simpler sentences: On the day of the November executions, machine guns began firing at the prisoners; they were used to clear the cells full of prisoners. Of the survivors there were three people who escaped and shared their memory of what happened that day in the prison.