No, we never find out who murdered the two assassins. However, in other threads over a year or two ago it was one of those topics that was discussed endlessly and I know that in those discussions I stated that Fredo would be the last of my suspects. So, if Michael also excludes Fredo, then once Fredo revelas himself as a traitor, Micheal has to figure that there are two traitors in the family.

However, in all these discussions about Fredo's complicity in Michael's attempted murder, one thing that we may have missed is Fredo's possible relationship with Geary or Turnbull. Remember when Geary meets with Michael and reveals that he has sources that have exposed Michael's proposed takeover of the Tropigala? I wonder if Geary's source was Fredo. Of course, unless I missed it, I don't think the film reveals a link between Geary and Roth.