Considering how Jack went from "nearly murdering two bullies" to "eagerly and enthusiastically partaking in a violent and bloody revolution", I'd say that covers sadism quite well. Jack very comfortably fits a rainbow of violent thug tropes, and is showing little to no remorse for his actions. In fact, he's fully prepared to commit [i]more[/i] crimes against his fellow man on principle, purely out of spite for the security force that dared to be overly-violent to him for his violent actions.

Jack's a fucked up boy, m8. Always has been, and always will. You could totally run with this shit. I'd call it a start of darkness, but his character profile kinda demonstrates that his story was plenty dark beforehand.