|“||Two of you will leave this room alive. One of you will die. You choose.||”|
— Younger's ultimatum
Marcus was born sometime in 1966 and raised in North Mammon, Pennsylvania. While in high school, he became the star of the town's football team. However, during the first quarter of the state championship game in 1984, he suffered a knee injury, which cost him a full-ride Notre Dame scholarship and presumably made it impossible for him to play again. After that, he lost a lot of friends and fell out of the social circle. As an adult, he became a garbage man; still carrying a lot of resentment towards his former teammates and friends within him.
"I never touched her. I never hurt them. I never even came into the room, Jeff. They did this. Brooke. Polly. All I did was... show them who they really are. What they were truly capable of. They were pretending to be decent. But when it came down to it... they reacted just the way I knew they would. They turned on each other. Just like when I got hurt. You all couldn't wait to run over me, to take my position, to take my life! And to forget all about me... You don't know what it's like, Jeff, you all had lives. I just cleaned up after you. Now you have to clean up after me."
In 2006, when the present-day North Mammon football team made it to the state championship again, Marcus devised a plan to make a point to everyone in the town and take his revenge on his now-mature former teammates. He abducts Brooke Chambers, Polly Homefeldt, and Kelly Seymour (three young soccer players and best friends) when they are alone in Brooke's father's house and takes them to a small basement in his house without any food, water, or chance of escape. He then instructs them to choose one of them to die in exchange for the surviving two to be released. Polly's mother, a friend of JJ's aunt, feels that there is something wrong, even though the girls had left phone messages, scripted by Marcus, and asks the BAU to help the local police.
As the investigation proceeds, Marcus has turned the parents of the girls against each other by planting evidence implicating Brooke's father and the girls' soccer coach, revealing their secrets in the process. When Kelly tells Marcus that they have made their choice, he simply drops in two hammers for Polly and Kelly to kill Brooke with. However, Brooke manages to grab a hammer and use it to kill Kelly. Satisfied by what had happened, Marcus releases the two outside of the police station and waits at his home for the police to arrive. When they do, he shows no remorse for his actions and remarks that he didn't touch them while they were in the basement. He said that all he did was "show them what they really [were]" and explains the motivations for his actions before Morgan promptly arrests him. Gideon is later shown to be disgusted and angered by Marcus's actions.
When Marcus abducted Brooke, Polly, and Kelly, he first grabbed Brooke outside the house, choking her with a garrote until she was unconscious. He then went inside and, holding Kelly at knifepoint, took Polly as well. He then had Polly and Kelly leave messages on their parents' phones, saying they had gone on a trip together (he didn't make Brooke do this since her father was out of town). He then took them to a basement in his house and tortured them psychologically and by starving them for several days. After a while, he gave them two hammers, one for each girl to use to kill the third.
Like all other predatory abductors, the unsub is intelligent, patient, and cautious, and this type of unsub likes to watch not only their victims, but everything related to them, such as their families and the authorities. He would thus keep an eye on the police and attempt to inject himself into the investigation. They also prepare a "nest" before setting their plans into work and abducting their victims, which could be a remote cabin or an underground bunker designed to confine and hide his victims once his abductions are done. The unsub also has a job that gave him access to Brooke, Kelly, Polly, and people related to them. He may also be a family member, a teacher, or a next-door neighbor.
- October 28, 2006: Abducted three girls and released two of them when the third was killed by one of them. They are:
- Marcus is the first unsub to successfully complete his goal. The others are:
- Frank Breitkopf in Season Two - A prolific serial killer and abductor who successfully killed at least 176 people, reunited with Jane Hanratty, and escaped arrest by taking a group of children hostage.
- Jonny McHale ("True Night") - A vigilante and serial-turned-spree killer who successfully killed Glen Hill (and possibly his entire gang), the leader of the 23rd Street Killers, the street gang that murdered his pregnant fiancé Vickie Wright.
- Boyd Schuller ("Reckoner") - A proxy killer who hired Tony Mecacci to successfully kill all the targets he wanted dead (including himself).
- Dylan Kohler ("Divining Rod") - A serial killer and abductor who successfully killed four women in order to make "the perfect wig" for Helen Garrett.
- Darlene Beckett ("The Pact") - A killer and proxy killer who along with Ellen Russell killed the men responsible for the rape and murder of Darlene's daughter, and killed the woman responsible for the death of Ellen's nephew. Darlene also evaded capture while Ellen was caught and incarcerated.
- Diane Turner ("Zugzwang") - A murderous stalker and abductor who successfully killed both her intended targets and herself.
- Anton Harris ("To Bear Witness") - A murderous abductor who successfully recorded his sister's torture and broadcasted it around the world. He also got his father's attention (but not his approval).
- Peter Lewis in Seasons Ten, Eleven, Twelve, and Thirteen - A "wound collector" and proxy killer who successfully killed Regan and the others responsible for a scandal that resulted in the death of his father.