Michael Chambers is indeed a murderer:; not of his wife, but of a one time student, Marcela Janowitz, who's work he'd ripped off.
Billy discovers that Kade witnessed more of the crime, and saw Michael moving Marcela after her strangulation. Billy figures out that Michael has buried her under his house, and he subsequently digs her up.
Chambers finds out, and chases Billy back to his bedroom justifying his crime. Kade shows up from his hiding place with Billy's friends. All of them say Chambers will have to kill them all, causing Chambers to break down.
As Chambers is taken away, Billy thanks his brother for helping solve this crime.
Thanks ND Woods!