Episode 8 ending twist (spoilers)
Just because Garrett has had possession of a knife that was linked to the killings doesn't mean he was the accomplice. He could have been hiding that, knowing that it was evidence and using it as a way to manipulate his father and/or protect the real killer.
I think there is still a lot to unravel, and can't believe the cop husband just jumped to that conclusion. I know, dramatic effect, but come on, that knife being found in an unlocked cabin that Garrett supposedly occupied does not equal proof of anything.
"You're so analytical! Sometimes you just have to let art... flow... over you." The Big Chill