What did the main charecter do for a living?

I couldn't figure out what the main character did for a living--yes, it was probably illegal, but the portrayal of what exactly he did was too vague. Also, why did he leave the dead girl's body there in the bathroom stall? What did he have to lose?
Over all, I like the movie. The best part was when he gave his sister such loving compliments at the end of the movie as he was leaving her apt.