“Wrath of Man” Question

So during the movie they portrayed this “Jan” guy as an unstable and problematic idiot. However towards the end of the movie he turned out to be this cold blooded killer and not afraid to take matters into his own hands and betray his own crew.

However when he returns to his apartment, he’s just like chilling in his underwear and when H casually threw some papers at him, He just stood there casually, reads it like a good boy and then gets shot and dies like a bitch.

What the hell happened my dude?