I don't understand the end yet. (Spoiler)
Almost at the end Gabe seems to be the killer because he attacks Sara.
But later Lucas show all the devices and recognizes to be the killer.
Why did Gabe act that way?
The Wikipedia says he thought Sara was the killer but this doesn't explain why Gabe shooted Lucas previously and why he fights again against Lucas after attacking Sara.
I think the scriptwriter tries to complicate things unnecessarily.
Why nobody saw the killer preparing the traps?