Because of the Cats by Nicholas Freeling. It's real:
Chief Inspector Piet Van der Valk of the Amsterdam police has a teenage gang on his hands: they are coming into Amsterdam from out-of-town, and they are remarkably professional. They leave behind a trail of wanton damage, senseless brutality, and rape, and one piece of possible evidence- 'the cats won't like it'. ""Because of the Cats was an international best-seller-indeed its group-murder plot was reenacted in real life shortly after, in Latin America-and Van der Valk acquired a huge following.""One copy with this cover at eBay. Via.
