I'm a relatively new parent myself...hhmm it is intense, people are uuhhhmmmmm  eliminated on screen but it is not a really gory or bloody film.  If he is a mature 9, I would think its ok. There is a scene that involves mob mentality which is probably the most frightening thing in the film, from my perspective.

It may be along the lines of the film "Signs" if that is of any help.

It could go either way, I suggest you see it first :-) .

I love being scared, my wife hates it and I had a good time and so did she.

Can you tell I don't want to be responsible for traumatizing your son ??