|Alias|| Billy Oak|
|Birth Date||February 6, 1967|
|Family|| Unnamed wife (deceased, killed by him)|
Connor O'Brien (son)
|Pathology|| Serial Arsonist|
|Portrayed By||Timothy Brennan|
|First Appearance||Public Enemy|
"Well, well, well. Does your mom know you're here?"
Born on February 6, 1967 in Providence, Rhode Island, William O'Brien was a "connected man" and sociopath who would commit arsons both for fun and profit, specializing in making them look like accidents caused by faulty wiring. In 1993, he set a fire that killed his wife and made it look like an accident in order for him to claim her life insurance. He was arrested on May 5 the same year. His then-10-year old son, Connor (who William had often abused), caught him in the act and testified against him, sending him to jail. William then spent 17 years in prison for arson and first degree murder. In 2010, his sentence was reduced to the possibility of parole in 2015. This drove Connor to become a serial killer, slashing the throats of random people in public places. After a month and three murders, the BAU was called in and were able to catch him, but not before he had devolved into a spree killer.
Ironically, Connor ended up in the same prison as his father. In the lunch line, Connor was handed a shiv by a fellow inmate and greeted William, who, unaware that Connor was armed, mockingly replied, "Does your mother know you're here?" He was then stabbed to death by a furious Connor while the other inmates idly watched.
Since the episode focused mainly on Connor, it is unknown as to exactly how William set his fires, but Garcia mentions that he would make them look like the result of faulty wiring.
- Five presumably victimless arsons
- Four arsons set for profit
- His unnamed wife (killed in a fire in order for him to claim her life insurance)