This list covers all minor criminals mentioned in Criminal Minds Season Fifteen.
Spectator Slowing
Wayne Beecher
A grave robber who sold a dead body to serial bomber Shelby Mattson, who used it as a surrogate for one of his targets in order to test a bomb.
The Manner Street serial killer
A serial killer from Montreal, Canada who rented a spare room in his house to pensioners and people on disability, killed them, and kept cashing their checks afterwards, claiming eight victims this way. When police discovered his victims' bodies in his basement, he killed himself in front of his home with a homemade explosive as they zeroed in. This element of his suicide was later emulated by serial bomber Shelby Mattson, who was the son of his final victim.
Karl Blair
The abusive father of serial killer Shelby Mattson who severely abused his wife Audrey and presumably his son too. Audrey eventually changed her name and fled with Shelby to Canada. His fate afterwards is unknown.
Saturday
Alexei Stanovich
A man living in St. Petersburg, Russia who sent harassing messages and death threats to Garcia, describing in detail how he planned to murder her. Due to him living in Russia, Garcia is unable to take action against him, causing her to take a stalking case extremely personally.
Ghost
Sarnicola Crime Family
A mob family based out of Chicago, Illinois that Louis Chaycon worked for as an enforcer before his arrest.
Robert Chaycon
The brother of serial killer and hitman Louis Chaycon, Robert was arrested along with his brother by Alvez for helping the former hide. He was later killed in prison by a rival gang, where his brother watched. His death was what motivated his brother to seek revenge against Simmons and Alvez, whom he blamed.
Date Night
Juliette Weaver's unnamed father
The father of future abductor and criminal accomplice Juliette Weaver, who killed her mother in a domestic dispute and subsequently evaded capture.
Rusty
Brenda Hacker
A social worker who took payments from fathers fighting custody battles to bribe family court judges to rule in their favor. She worked with future serial killer George Kyle Peters and covered up his history of alcohol abuse. After his son was killed in a car accident with him, she called him when he woke up from his coma and changed the circumstances of the accident, adding that he'd slipped on black ice, in order to protect herself and keep people from digging into George's past and finding the coverup.
Face Off
Orlando Gaines
A private detective who was fired from his job as a Concord Bay narcotics cop, as he sold police confiscated drugs and served five years in prison for the crime. He was hired by Everett Lynch to locate Lynch's father Delvin Weaver. Lynch later killed Gaines and set off a fatal home explosion to use Gaines' remains as a brief distraction for Lynch to fake his death.