It's often felt and stated that Rocco betrayed Michael in II, that he was the one who killed the would-be assassins. Why is this so assumed?

People seem to take Michael sending him on his suicide mission, and Rocco accepting it, as Michael offering Rocco a chance to atone, and Rocco accepting it is him accepting the offer of an "honorable death" ala Pentangelli - but could it not just be Michael didn't really care if Rocco came back alive or not; he was just a soldier, small potatoes, a pawn, a useful tool. He wasn't Al Neri. Rocco was a good soldier, and what he was going to do - say no? He saw Michael was ready to take out anyone he saw as potential enemy, lashing out publicly at his own "brother" Tom. So, you'll say no to that man?

It's stated in the film that Fredo had a crew. So, could it not have been one of "Fredo's people" who killed the assassins?

Perhaps Rocco failed in bringing the would-be assassins back alive, but Michael already figured they were dead before he ordered them to be be found alive. "If I'm right, they're dead already." So I don't think he sent Rocco on a suicide mission to atone for a failure of something he foresaw as being inevitable, anyway.

I never accepted this theory. We all know Michael's character; if he even suspected someone of being complicit in an attack on his family, that person would be fish food in a matter of minutes. Rocco was head of security though, and the attack showed a real failure in the system. Maybe he felt he needed to atone for that failure.

As for who killed the assassins, well it had to be Fredo, as far-fetched as that seems. Nobody else fits the story. It's a real failing in the plot construction.

No question that Fredo ,at the very least opened the drapes.

However,the one theory that I can't quite swallow is that Fredo killed the assassins on his own.

Could weak,stupid,and bumbling Fredo (remember the scene where Vito was shot,and he dropped his gun) have gotten the drop on two professional killers ?

So for me,the bottom line is that Fredo had to have at least one other person in on the plot. Maybe Rocco,maybe one of Fredo's crew,hell maybe even Fredo's wife( that little farce she played after the shooting could nave actually fooled a Corleone)

As far as Rocco being sent on a deliberate suicide mission,remember that Tom was against the hit on Roth. Mike says that "if history has taught us anything it's that you can kill anyone" Mike then turns to Rocco who replies "difficult,not impossible". It's almost as if Rocco wants to one-up Tom,and impress Mike. I wonder what would have happened if Rocco would have said "Tom's right Mike, with all the heat on Roth it's too risky.We can always use our connections and our people to get to him in jail.

I think Rocco was too stupid to keep his ego in check.

I also never bought into Rocco-as-traitor. I think Michael was manipulating Rocco into accepting that almost certain suicide mission. After thoroughly dissing and humiliating Tom, he comes out with "you can kill anybody"--and then asks, "Rocco?" What was Rocco going to say--"Uh, nope, Mike, I ain't doin' it."

Maybe Michael was punishing Rocco because the Tahoe attack and the killing of the two NY hoods happened on his watch. More likely: Michael simply viewed Rocco as dispensable. One of Michael's many vices was self-centeredness: Rocco was Clemenza's protege, not Michael's, just as Tom was Sonny's choice for brother and Vito's choice for consigliere--not his.

As I wrote, it's a real failure in the plot construction. Surely Coppola recognised the massive hole?

How's it a hole though?

Fredo is established has having a crew, even if they're of Mickey Mouse guys. Maybe Fredo really did know SOMETHING was gonna happen - maybe, say, a kidnapping, rather than a hit. He has his guys make sure the assassins get access to the Tahoe compound. When he realizes he was duped and it's a hit, he has his guys do the would-be assassins in to protect his own ass.

Fredo is revealed as the traitor, so I mean, he's the only one with motive to have the assassins knocked off.

A long time ago, I (warily) came to that conclusion, by (weak) default--no other likely suspect, he was the traitor, had to cover his ass, presumably had men under his command. But, I can't defend it: The weakness of that theory is that it went down far too quickly for Fredo to realize he'd been duped, decide what to do, and organize his men to kill the attackers.

I've often thought that, if I had the opportunity to ask FFC one question, it'd be: "Who killed the Tahoe shooters?"

I agree with Turnbull.

I think it is entirely reasonable to suppose that Rocco would have spoken with (ie. interrogated) all of the men in the compound to find out who heard what, who saw what, and when. As head of security he would be derelict in his duty not to do so, or even more so. If people from Fredo's crew carried out the killings, it would have been found out. Why wasn't it found out? Because Rocco wouldn't have spoken to Fredo. Not the bosses brother. He would have been above suspicion. It all points to Fredo being the killer, which everyone agrees is ridiculous.

As I wrote, it's a massive failing in the plot construction.

I also “never bought into Rocco-as-traitor”

If there was the slightest suspicion Rocco was the traitor, I believe there was no way Michael would have let Rocco live let alone continue to be in charge of security and safety of the compound and the family - “trusting [Rocco] with the lives of his wife and his children - the future of the family”

Rocco linked to Michael
The Godfather Novel What did Don Vito Corleone see in Rocco Lampone

Neri been already picked for Fredo's killing So it is logical Rocco gets picked for Roth's Killing

Not if Fredo knew it was a hit and was prepared for it

It was the assassins who were duped
Say if the assassins were told to wait by Fredo and Deanna's bedroom [where their bodies were found - Right out their window lying there dead] for Fredo to hide / smuggle them out but were always going to be killed – Dead men tell no tales

I can answer that! Fredo!!

Tom and Fredo

The assassins would never have suspected the “ineffectual dunce” had it in him and would have been sitting ducks!
Perhaps Fredo did have it in him!

incoming Don Fredo was playing the victim not a real man, I can't control her, Mikey and milking sympathy all the while knowing Michael would be dead that night

Fredo is the traitor