Audio problem: When Logan explains how Edgar killed Logan's wife, the camera is an over the shoulder shot looking at the cop. Logan's mouth isn't moving. (01:18:05)
Audio problem: When Halloran and Hunt are discussing orders from the commissioner to exhume Jigsaw, it's clear that several of Halloran's lines have been looped in post. His voice is a bit too loud and a bit more forceful than he appears to be speaking, and at least one word doesn't quite line up with his mouth movements. It can be hard to spot the first time, but if you look for it, it's noticeable. (Confirmed in DVD/Blu-Ray commentary - the actor lost his voice and his lines had to be looped).
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