In part one of this series, I detailed how the U.S. Department of Justice has focused its attention on the aggressive investigation and prosecution of “pill mill” cases. See “Part One: DOJ Devotes Resources, Vows to Come After ‘Pill Mills.’” In part two, I discussed what consequences doctors and other medical professionals could face as the result of a “pill mill” investigation. See “Part Two: What’s At Stake for Prescribing Professionals in ‘Pill Mill’ Cases.” In this installment, I give a detailed explanation of how the government investigates these cases.