Why highly unlikely???..... Don't you believe that they would have a patsy ready to be the scapegoat?
If by 'they' you mean the assassination conspirators rather than the post-hoc 'investigators', then the evidence is they made no effort to set Mr Oswald up as a gunman, let alone a lone nut gunman. That was the impossible job of the 'investigation'. Which is why the Warren Report is such a joke!