Former FBI Special Agent John Grusing on his new book, "The Devil I Knew"

Jonny Grusing was a Special Agent (SA) with the FBI’s Denver Division from 1996 to 2021. For 23 years of his career, he worked violent crime matters to include missing persons, serial killers, federal jurisdiction homicides and mass attacks. From 2008 until his retirement, he served as the Behavioral Analysis Unit (BAU) Coordinator for the division. SA Grusing received extensive training from the profiling unit during these years and employed that training in addressing the serious violent crime cases in Colorado. From 2013 through the present, he has taught hundreds of seminars on profiling serial killers and preventing mass attacks using the sound BAU principles. He is now Director of Security for the Douglas County School District in Colorado.