In this special 100th edition of Cold Case Files, we look at the biggest serial murder case in U.S. history - the 20-year hunt for the Green River Killer. Dave Reichert, the detective who made finding the killer his obsession, walks us through the case. He tells vivid, sometimes harrowing stories about the murders, saying, "You never forget the sight of a 16-year-old body lying on her back on the riverbank with ligature around her neck." Reichert headed up two Green River task forces until forensic DNA technology helped crack the case and brought him face to face with the killer thought to be responsible for 48 deaths.