This list covers all minor criminals mentioned in Season Twelve.
The Crimson King
Earl Roy Everton
One of thirteen serial killers who escaped from prison during the events of The Storm. He attempted to flee to Mexico with the help of an accomplice, but was recaptured through the efforts of Luke Alvez, who lured him out by posing as a coyote.
Carla Jean Birch
The accomplice of Earl Roy Everton, who attempted to help smuggle Everton into Mexico. She was arrested by the BAU after an undercover operation led by Alvez.
Brian Phillips' first foster parents
The couple of the first foster home of Brian Phillips, who was regularly attacked with broken bottles and shards of glass by his foster parents. The couple's daughters consoled him every time, which led him to retain the two girls as alternate personalities due to Dissociative Identity Disorder once he was transferred to the more loving home of Gail and Bob Phillips.
Sick Day
Unnamed Seattle spree killer
An unidentified person in Seattle, Washington, who went on a killing spree with an assault rifle. He or she was somehow tracked down by the BAU and either killed or arrested.
Keeper
Curtis Burton
The abusive father of Cormac and Todd Burton, Curtis would also abuse his wife and force his sons to wear dog muzzles, sleep in a slaughterhouse and watch him kill pigs, all while telling them they were next. He later forced his sons to abandon a dog they found. Curtis later died of a heart attack in 2015, which was the trigger for Cormac's serial killings.
Scarecrow
John Decker
The abusive father of serial killer Kevin Decker, John was a highly religious and misogynistic man who severely abused and punished his son. When Kevin fell in love with a girl named Wendy Baldwin, he kicked Wendy out, whipped Kevin in the back, and then strapped his son to a cross in the middle of a nearby cornfield, like a scarecrow, hung a sign around Kevin's neck that said "fornicator", and left him there for the night. Kevin finally snapped and killed John, hanging his body in the same way. His actions traumatized Kevin and caused both his psychosis and subsequent serial killings.
Profiling 202
Belgian terrorist cell
A terrorist cell of unknown ideology that operated in Belgium. Stephen Walker created a profile for them, but it turned out to be wrong and three undercover agents were killed as a result. However, the cell was still stopped before it could carry out a bombing at a major soccer game.
Seek and Destroy
Zeke Daniels' unnamed aunt and uncle
The abusive relatives of gang leader and later serial killer Zeke Daniels, they were presumably his maternal aunt and uncle (on his drug-addicted mother's side). Nothing more about them is ever specified, including if they were ever prosecuted for the abuse they dealt to their nephew.
Surface Tension
Fred and Marnie Jarvis
The parents of serial killer Bryce Jarvis, Fred and Marnie formed a religious movement and were apparently its only members. They presumably abused their son sexually, which led to numerous calls to Social Services claiming abuse (presumably made by Bryce) but they were never proven. The two were later arrested for fraud and jailed for six months. On April 27, 2015, Fred and Marnie were killed when their home was swallowed by a sinkhole. Their actions were ultimately the cause of their son's psychosis and fixation on Satanism (and subsequent killings).
A Good Husband
The D.C. Torso Killer
A still-unidentified serial killer who was active in Washington, D.C., in 2004. He targeted prostitutes, killing them and dismembering their bodies post-mortem, with only the torsos being found, a la the Mad Butcher of Kingsbury Run. The BAU profiled the dismemberment as a forensic countermeasure to prevent identification of the victims, and that the killer was no longer active because he was locked up for an unrelated charge. In 2017, he was believed to have resurfaced after a new torso is discovered in Palm Springs, California, but was ruled out after the victim was revealed to be a real estate agent and not a prostitute.
Unnamed hitman
A hitman who was hired by a woman to kill her husband, Rossi's friend Judd Ray, during a longstanding domestic dispute. However, Judd survived the hit. The case was brought up by Rossi and Alvez as an example of wives going after their husbands during domestic disputes.
Spencer
IRT Costa Rica case
An unspecified case that the International Response Team was deeply working on in Costa Rica during Reid's arrest in Mexico.
Miguel Santos
A Mexican criminal who was being transferred to Carcel Gran Negra on an unspecified charge(s).
Victor Ramirez
A Mexican criminal who was being transferred to Carcel La Montana on an unspecified charge(s).
Juan Zamora
A Mexican criminal who was being transferred to Prisión de Máxima Seguridad El Diablo on an unspecified charge(s).
Oscar Mendoza
A Mexican criminal who was being transferred to Santa Adeladia on an unspecified charge(s).
Alpha Male
Milos' gang
A small gang of inmates under the wing of Milos. They consisted of Hicks, Dwayne, and Little T. They appear to be white supremacists, but it is unknown if their leader aligns with that ideology as well. They later assisted Milos in his attempt to kill Reid, but all four stood down at the behest of Calvin Shaw.
Elena Olegnova
An associate of the Russian Mafia. She was bribed to help Calvin Shaw and his team infiltrate the organization. It was originally assumed that Olegnova got greedy and started blackmailing the team, threatening to blow their covers if they didn't increase her paychecks. Believing an arrest would endanger the lives of his undercover teammates, Shaw chose to kill Olegnova to silence her, and pin the murder on a rival gang. However, Alvez later deduced that Elena was having a romantic affair with the already-married Shaw and he killed her when she got pregnant with his child.
Cidro Torres
A prisoner who was scheduled to be moved into the Protective Custody Unit. What he did to merit being sent to prison is unknown.
Rex Driskill
A prisoner who was scheduled to be moved into the Protective Custody Unit. What he did to merit being sent to prison is unknown.
Tyrone Fletcham
A prisoner who was scheduled to be moved into general population. What he did to merit being sent to prison is unknown.
Ernest Zaffross
A prisoner who was scheduled to be moved into general population. What he did to merit being sent to prison is unknown.
Lamont Wexler
A prisoner who was scheduled to be moved into general population. What he did to merit being sent to prison is unknown.
Delmar Wauford
A prisoner who was scheduled to be moved into general population. What he did to merit being sent to prison is unknown.
Treyvan Hillis
A prisoner who was scheduled to be moved into general population. What he did to merit being sent to prison is unknown.
Hernando Quintana
A prisoner who was scheduled to be moved into general population. What he did to merit being sent to prison is unknown.
In the Dark
Samuel Gordon
The father of later serial killer Trey Gordon, Samuel abused his son and was arrested for various crimes, including solicitation of prostitutes, drug use, and he was also a poacher. He frequented brothels and took his son there too (which led to Trey being molested by prostitutes). One such brothel was raided when Trey was eight and being molested by a prostitute. Whether or not Samuel was arrested or not is unknown. He died of a heart attack on February 7, 2017. His death was the trigger for Trey's murders.
Unnamed prostitute
A woman who molested Trey Gordon while his father was in another room having sex with another prostitute. She was caught naked and molesting Trey during a police raid of the brothel she worked in, though it is unknown if she was prosecuted.
Louvre case
An unspecified case Prentiss and Stephen previously worked on together. Stephen was uncertain about the perpetrator being found guilty, but Prentiss told him to have faith in judicial system. In the end, the perpetrator was convicted.
Unforgettable
Dmitri Sobchek
A former Russian national who once assisted Stephen and his friend at the BAP, Sam Bower, in their investigation into corruption in the Russian government. He is now an American lobbyist for Russian oil interests, but is currently under investigation for bribing Congressmen. He was considered a suspect in a series of radiation poisonings, but he admitted to Rossi and Prentiss that he was now sympathetic to the Russian government and that he wouldn't be acting alone if he was truly the unsub. He was later exonerated when his alibi checked out.