2) Fredo had been in Las Vegas for more than ten years. He had known Moe Greene. It seems improbable that he didn't get to know Roth and Ola during that time.
This indeed suggest he must have at least seen Roth and Ola as they were closely associated with Moe Greene.
But that doesn't mean that Michael would have also known this.
"It was between the brothers Kay -- I had nothing to do with it."
