Q:

Movie with "White box dimensions" where woman is shot at the end

My dad was watching a movie on TV roughly 15 years ago (maybe a little less), where people were dying in what looked like "White box dimensions".  I say this because that's what it looked like, from what I remember it looked like a group of people were trapped in an all-white space where they were dying one by one.  I think there was an old man who got ripped apart by some mirror-like transparent prisms. 
Sorry for the rough details, I was a bit young when I saw it.  The one solid detail I remember is that at the end the last surviving woman appeared to wake up in some shallow water.  After she woke up she was met by some government agency looking type men, one of whom shot her in the head. 

A:

This is Cube2: Hypercube from 2002. 
The ending matches your description.  A woman escapes a futuristic dungeon and is executed by MiBs. 

and in this clip, you see a guy being ripped to shreds by prisms.