William Duke Mason

William Duke Mason was a serial killer and rapist who appeared in Season Eleven of Criminal Minds.

Background
Mason was raised by his parents Jeff Koldyke and Violet Mason in Dallas, Texas. His father apparently left the family, and Violet took him to Las Vegas, New Mexico, where he spent his junior year of high school. He came to hate his current lifestyle in the town and began interacting with the wrong crowds. While in school, he became romantically involved with a girl named Tammy Mae Vasquez. However, their relationship was apparently strained due to his high-risk lifestyle and his sketchy friends. At some point during their relationship, he unknowingly impregnated her. Mason then dropped out of school and ran away from home, later meeting Benjamin Wade and adopting his biker lifestyle. In 2009, the two began a crime spree together, starting with a robbery and mass murder at a burger shop that left four teenage employees dead. Then, they traveled to Texas, where they robbed an El Paso gas station and Wade killed the clerk.

However, they were arrested by police while trying to set fire to the station. Wade was given a lengthy sentence for his murder of the clerk, but Mason was sentenced to six years for his participation. They were both incarcerated at Texas State Prison, where they shared the same cell block as Lester Turner, who was imprisoned since 2004 for a rape and assault in Lubbock. Mason saved Turner from being shanked by another inmate, and they became close friends since then, with Mason apparently coming to neglect Wade in favor of Turner. Turner was eventually released in 2014 after completing his sentence, and one month prior to "Outlaw", Mason was also released. The two then opted to commit a crime spree in the same vein as the original followed by Mason and Wade before their 2009 arrest. All the while, Mason remained unaware that Tammy had given birth to their son, who she named Cole and left under the shared care of herself and her mother Ruth.

Modus Operandi
During his robberies and killings, Mason always operated with a partner (initially Wade, but then switched to Mason following their releases). During the Burger Corral robbery, he restrained the night staff (all teenagers) right after closing hours (the males were blindfolded and tied up with their own belts and electrical wires, while the females were tied up with her own underwear), separating them by gender to establish dominance, raping the females, and killing them with single gunshot wounds to the head fired by a revolver. He then set fire to the restaurant as a forensic countermeasure. He repeated this process during the Dee's Original Diner robbery, although this time, the victims (also teenagers) weren't separated and were instead killed while facing each other, which was Mason's signature.

Known Victims

 * Unspecified date in 2009, Las Vegas, New Mexico: The Burger Corral robbery :
 * Two unnamed teenage boys
 * Jenny Tanner
 * Unnamed teenage girl
 * 2015, New Mexico:
 * October 19-20, Las Vegas: The Dee's Original Diner robbery :
 * José Rivera
 * Eddie Butler
 * Renee Acosta
 * October 21:
 * Unspecified locations:
 * An unnamed man and his son
 * Lester Turner
 * Las Vegas, New Mexico: Ruth Vasquez
 * Unspecified location:
 * Tammy Mae Vasquez and her son Cole
 * Shot at the following repeatedly, but missed:
 * Derek Morgan
 * Spencer Reid
 * An unnamed police officer

Appearances

 * Season Eleven
 * "Outlaw"