America’s greatest unsolved mysteries are explored through interviews, archival footage and re-creations. Recently unearthed evidence and intriguing, new theories bring each case closer than ever to finally being solved.

An Unexpected Killer takes a wild and unpredictable journey into homicide investigations where the true identity of the killer comes as a shocking surprise. Combining unparalleled access, captivating interviews and stylish reenactments, each investigation starts in a familiar way – examining the crime scene, interviewing potential suspects… but then something unexpected changes everything. A new witness, an overlooked piece of evidence or even an innovation in forensic science sends investigators on a totally unexpected path that ultimately leads to the conviction of the real killer.