Important Q

Rating: Null/10 (23 October 2006)

in the end i guess it turns out costello was an Fbi informer. but who the hell did he inform on? wasn't he at the top of the mob? and if not who was above him? it doesn't make any sense. and who was that guy who shot dicaprio at the end? where did he come from? and why did he shoot the black cop? was it important for the fully understanding of the plot? and if he helped daimon, why did he shoot him after wards? i think these questions are important to fully understanding what the film is about. not explaining these details is unfair to the audience. i would love it if someone will explain that to me. i really loved the movie but not knowing these details kind of ruined it for me. thanks in advance.