I remember they did say he ended up killing the boss of the international gang before. they mentioned this before. so that explains why he's at the top. I thought he built his own gang from scratch but he just usurped someone elses place. It looks like he killed his own girlfriend I bet.
his fascination with animals tho...he feels he's the only human and when it comes to other people he treats them like animals? weird that he doesnt have any background of him abusing or murdering his own pets tho to make it clear.