Liam was born into a very wealthy family. His Father was a stressed out alcoholic who owned an aerodynamic engineering company that was contracted out of country and led him to be out of country for most of Liams life. His mother loved him alot, but due to her husband being an alcoholic, and always gone from the US, she made the mistake of double dosing her depression meds on top of alcohol in hopes for a mental escape, and passed away when Liam was 11.
This crushed Liam. His father being the alcoholic he was couldn't handle his wifes untimely passing and unrightfully passed the blame onto Liam as often as he was home.
Liam took this horribly and couldn't understand why his affectionate mother would do such a thing because of him. His mental state suffered and Liam became a very angry boy, feeling betrayed by his mother and father. He often did things that showed characteristic of a budding serial killer, like kill small animals and convincing other school children too do horrible things.
When he was 16 his father had been through programs to help him with his alcohol addiction. In a sober change of heart his father flew him to Chernarus to be with him while his company worked on craft for the CDF. Upon arrival Liam found out his father has relapsed and comitted suicide, and that's when the outbreak spread through Chernarus.