This paper considers an extensive cartel contamination of markets in the Dutch construction sector. Overwhelming legal evidence of bid rigging in this sector was obtained in 486 leniency applications in which complete secret accounts were submitted. I offer a case study and a broadly based post mortem of methodologies that were applied earlier to detect malfunctioning markets in the Netherlands, but failed to identify the construction sector as problematic. It is concluded that these studies were seriously flawed. Theoretical and empirical economic forensics (if properly applied) creates value for antitrust authorities in detection of antitrust violations directly, or by informing them where to look for direct evidence.