They weren't shot. I believe that we've all come to the conclusion that they were garrotted (If you look closely, you can see the marks around their neck).

Also, there's certainly no way that it would have been "easy" for Fredo to kill them.

Here's the case against that scenario:

1- Weak Fredo, getting the drop on two professional hired killers, and garrotting both?

2- How could he have done it so quickly and without being seen? Immediatley after the shots are fired we see lights go on, and guards and dogs running around like crazy.

In fact, I don't believe that there's any scenario in which anyone could have killed the hitmen without being seen, unless that person was standing right there with the shooters while they were shooting.

And even so, assuming that they weren't shooting from the ditch in which they were found, how were they killed and dragged there so quickly without anyone seeing any of this.

Possible Answer: The drainage ditch or whatever it was was their escape route. Whoever killed them knew that and was waiting for them there. Fredo? Doubtful.

3- If you believe that Fredo "didn't know it was gonna be a hit" (and if you think he did know, then you have to provide an explanation for what he meant when he said to Ola "You guys lied to me."), then how could he have been prepared to kill the hitmen, much less accomplished it? He didn't even know that there would be hitmen to kill.

4- These two guys were killed so quickly and efficiently after they did their shooting, that killing them must have been part of Roth's plan, whether Michael was killed or not.

Reason? Again, because they were killed too quickly and efficiently.

The reason that they were killed could not have been simply because they failed in their mission, because whoever killed them did it so quickly that I don't see how he could have known that Michael was still alive.

I doubt if an old shrewdie like Roth was depending on a bumbling fool like Fredo to kill two professional killers.