At some point in Mayford's life, her father Earl died from unspecified causes, her mother Tiffany committed suicide for unknown reasons, her brother Doug died in a motorcycle accident in 2002, and her aunt Trisha was committed to a psychiatric ward for mental illness or defect. Brian Cochran revealed that, as an adult, she received her training (and likely her bomb-making skills) from Mossad. She eventually became a hitwoman and member of a network of hitmen that cropped up after the dismantlement of the Silk Road by the FBI in 2013. She was hired by Cochran to kill a bureaucrat who had forgotten to pay him a bribe on time. As a result, on August 13, 2015, Mayford killed a total of at least 173 people, including the bureaucrat, in several explosions at a container storage station in Tianjin, China.
In 2015, the BAU began investigating the network after it set its sights on Garcia. When they began to close in on them and two of their own are killed, Mayford hatched a plan with Cat Adams to attack the BAU. She came to Harry & Glenn's Grill and Bar with Cat before Reid and the others arrive. As Cat takes Reid hostage, Mayford operates secretly, setting up explosives powerful enough to destroy an entire city block and kill thousands. After a while, Mayford prepares to detonate the bombs. However, she is found by Morgan and Lewis, who deduced her gender earlier. The two agents subdue her and grab away from her the phone she planned to use to set off the bombs.
Mayford would kill the victims in her contract kills by using bombs, hence her nickname. It is likely that she would be contacted and paid by her clients with each contract kill. Exactly how she committed the container storage station chemical explosions is unknown. During the attempted Harry & Glenn's Grill and Bar bombing, she used several C4 bombs attached to the restaurant's gas pipelines, which would cause an explosion powerful enough to take down an entire city block.
No official profile of Mayford was made by the BAU, since they focused on the network as a whole. Although it was initially believed that Mayford was male, the BAU switched their focus on women from the implication of Cat's comments about gender bias. They also briefly described her as being extremely paranoid due to her usage of explosives in her contract kills.
- Killed numerous unnamed victims prior to Entropy
- August 13, 2015, Tianjin, China: The container storage station chemical explosions (hired by Brian Cochran to carry out the hit):
- The following were killed:
- Unnamed bureaucrat (target victim)
- 172 unnamed people
- Eight unnamed people (possibly)
- 797 unnamed people (all injured)
- The following were killed:
- January 13, 2016, Washington, D.C., U.S.: The attempted Harry & Glenn's Grill and Bar bombing:
- With a final body of over 173 people, Mayford is one of only eight unsubs in the show's history who are confirmed to have claimed the lives of hundreds. The others are Vincent Perotta (who killed hundreds of people, with an exact number unspecified), Frank Breitkopf (who killed at least 176 people), Billy Flynn a.k.a. "The Prince of Darkness" (who killed approximately over 200 people), Thomas Yates a.k.a. "The Womb Raider" (who killed at least 103 people), Hayman Vasher (who killed 151 people), fellow hitwoman Cat Adams a.k.a. "Miss .45" (who killed approximately over 200 people), and Jake Logan (a serial killer who killed approximately over 379 people).
- Though Mayford's true name and personal background were never revealed in Entropy, they could be seen on a spreadsheet the BAU made of the network and a group of operatives-for-hire that abducted Morgan in Derek. This spreadsheet was seen in The Sandman and A Beautiful Disaster, and the show's Twitter account also released a photo of the prop in one of its posts while promoting the latter episode.
- Mayford is partially similar to Izzy Rogers, a criminal who appeared at the end of Season Seven. Both were prolific, female serial bombers and international criminals who targeted victims all around the world and were members of ragtag criminal groups. Both also engineered a standoff against the BAU and other authorities in Washington, D.C., with accomplices; both standoffs involved dozens of hostages, including a member of the team, and the use of explosives, though Izzy was successful in detonating hers.
- Mayford is the first unsub on the show to be responsible for a real-life event that resulted in casualties, let alone one whose case already seemed to be solved.
- Mayford has the largest number of would-be victims out of any unsub in the series, having tried to kill more than 1800 people.