Complex sentence: A year later, on the anniversary of Dłużewski's death, the group declared that they will kill all policeman they see on the streets--on that day, 75% of the police officers did not turn to work.
Split into simpler sentences: A year later, on the anniversary of Dłużewski's death, the group declared that they would kill all policeman they saw on the streets. On that day, 75% of the police officers did not turn to work.