Who would be deemed responsible for the massacre?

Tricky explaining! how Tessio, the sole survivor, was miraculously spared

Whilst we know! Tessio is a “dead man sooner or later” - wouldn't it become known that Barzini was somehow “connected to Michael's murder” that “Tessio did conspire with Barzini to whack Michael”

Seems far-fetched....however I suppose who is left in the Corleone family to hold Barzini &/or Tessio accountable even if Clemenza and Rocco were not killed simultaneously Big ask indeed

Turncoat Tessio believes he can set his Don up to be murdered and another Don will embrace him into their family

Oh, Tessio—you [even bigger] stunad!