Thank you for the compliment, Turnbull.

In some ways, I think your rejected theory ties in with mine. True, Tessio doesn't need a war with Barzini, and I think if Barzini is allowed to know that Tessio whacked Michael, it puts Barzini on high alert. Tessio can't win in that situation at all if Barzini lives. Tessio either gets hit by Barzini outright, or one of the three key leaders in the Corleones gets him. Tessio needs a patsy to lay Michael's death on, and Barzini is perfect for that.