Continuity mistake: When Logan is shown the message found on the second victim, the string in the evidence bag attached to the note changes between the close up and the far shot. (00:28:30)
Continuity mistake: When Carly dies we see her fall down onto the right side of her face. Camera cuts to a close up of the blood pouring out of her ears and neck, and she is lay on the floor on her left side with her right side of her face upwards. (00:20:30)
Continuity mistake: The amount of blood on the memory card Logan finds changes between shots. (00:12:30)
Continuity mistake: At the start Edgar smashes his car up and kicks his window out and jumps out leaving a bit of glass in the window frame. However after the camera changes, the 2 bits of glass have disappeared. (00:01:05)
Continuity mistake: As Anna and Mitch get trapped in the silo, various sharp and pointy tools begin to fall on them (a pitchfork, circular saw blades, nails, etc.), but when Ryan finally pulls the lever and the silo door bursts open, they all disappear. Only the wheat and the trapped duo can be seen "flowing" out.
Answer: Spoilers: As revealed at the end, Halloran is a crooked cop who has a past connection to Edgar. Edgar therefore wanted him there, since he presumably assumed Halloran could help him out of this jam. It's also possible that Edgar's tape instructed him to find Halloran, but we can't know this for certain, since it wasn't on-screen.
TedStixon