Fredo DIDN'T know that it was going to be a hit. I simply do NOT believe that Fredo was heartless or ruthless enough to have his own brother killed so that he could take over the family.
I've said this several times over the years ; After the hit attempt on Mike, what does Fredo say when Ola calls him?
"You guys lied to me."
He didn't knoqw that it was going to be a hit.