It's too obvious who the killer is for the wrong reasons (spoilers)
Okay, if you're smart enough, you will see plenty of clues pointing to Lucas (Miller) being the killer- he doesn't drink the coffee, his reflection can vaguely be seen when he kills Kilmer's character, he is directly tied in with every death of event (like telling that one dude to turn off the water).
But for me, it was even more obvious for another reason- No one ever suspects him. It's a common conventional that the killer is the last person the movie throws suspicion on. Just look at the order.
1) Gabe (LL Cool J)- The first major suspect. A clue that he's probably innocent is he's trying to explain himself, but these so called geniuses keep interrupting him.
2) Rafe- While only brief, he's accused because he was the one who made the coffee.
3) Vince- I don't know the order of this, but Vince briefly comes under suspicion twice- when he's acting creepy towards LL Cool J and when he refuses to give up his gun. Also, him knowing the lost colony story disturbs Gabe.
4) Bobby- When he's explaining how the killer must know his *beep* everyone turns towards him, suspecting him for that reason. Then he dies.
5) Nicole- I don't really know if Nicole was ever a suspect, but the movie starts treating her actions with suspicion. She acts trigger happy and even Gabe says if she leaves, she wont be let back in.
6) Sara- Obviously.
7) Harris (Kilmer)- since his voice starts playing on speakers.
The only time Lucas is suspected at all is when Nicole points out he mentioned the water (leading to Bobby's death), but his line diffuses that pretty quickly. In essence, even when I saw this in 2004, I knew Lucas was the killer because the movie kept throwing its suspicion on everyone else.
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