I would suggest another theory.
Look at the dynamics of the characters and how they consistantly interact with one another.
My theory, Michael Scott is the scranton strangler.
A. His dynamic relationship with Toby Flenderson is one of protagonist vs antagonist. Michael Scott is constantly being told he can not do things he wants to do by Toby who runs human relations. The fact that Toby was put on the jury places him in his constant position of telling Michael Scott no, as in, you can not frame this man.
B. George Howard Scub's initials are GHS which in an annacronym for "geek in high school", which we know Michael was but Phyliss's recounting. he was a loner in high school and that description gets used often when describing serial killers or mass killers.
C. In the movie, Threat Level Midnight, we actually see Michael strangle Oscar. His alter ego Michael Scarn unecessarily kills Oscar's character by strangulation, and when the employees see this scene they looked at each other uncomfortably.
D. Also, i would suggest this character was created by Bj Novak, and upon his leaving the show, this odd ending to the character was written to wrap it up and attempt to put it to and end. I believe it was a subplot that a writer like Novak would be clever enough to keep alive throughout his tenure.
Just something i pulled out from deep, however, this is my conclusion.