Lou became acquainted with the Reid family as the father, William, coached the local Little League baseball team, in which his son, Riley, was a member. When Riley was found raped and murdered, Lou became distraught. When the Reid mother Diana found out that a man was stalking her son Spencer, she alerted Lou, who, in turn, looked into Gary's history and recognized him as a pedophile. Outraged, Lou called Diana and told her to lead him to Gary's house, which Diana did so. Bringing along a baseball bat, Lou stormed inside the house when he and Diana arrived and beat Gary to death in a fit of blind rage. Diana stumbled across the scene and managed to get some of Gary's blood on her. She apparently let Lou go, and when William found out, Gary's murder was kept quiet, but this haunted either William or Diana (it is unknown as to who was more traumatized than the other), causing the both of them to divorce.
Decades later, after having nightmares of Riley's death while investigating another case, Spencer and the BAU reopens the case, even interrogating Lou, who informs Spencer of the location of William's workplace. Later, they discern that Gary had been murdered and Lou was the killer. He is arrested later while he is working. While being questioned, he is avoiding the questions to protect Spencer's parents until they come to the police station themselves and reveal to Spencer what really happened. He is likely incarcerated afterwards.
Since Lou only killed one person, the term M.O. is misused. He confronted Gary at his home and beat him to death with an aluminum baseball bat. Other than that, no other details of how Gary was killed were disclosed.
No profile of Lou was made by the BAU, since the team was focused on Gary.
- 1984: Gary Michaels