Dennis Rader

Dennis Rader, a Kansas serial killer, a.k.a. the BTK Killer, installed alarms as a part of his job, and many of his clients had booked the company to stop BTK from ever entering their homes, unaware that BTK himself was installing them. He was finally caught after sending a 1.44MB diskette to the police - which they told him was untraceable - containing metadata from a deleted MS Word file.