Well that is because the case was never solved. You have to decide for yourself what must have happened. Did he kill himself or was he murdered and if so who are the likely killers. It was also a statement about cover-ups and trying to go up against the powerful. I also loved the 50's sets and costumes. Very authentic.
p.s.: as a superman fan as a kid I loved seeing the superman filming stuff. worth it just for that. I remember watching superman after school on an old old big box tv.
The Black Dahlia
is unsolved, too, but I bet
DePalma solves it . . .