When confronted, Fredo does his "I didn't know it was gonna be a hit!" routine but he says something that he was told by Ola that it was going to be a kidnapping.
FREDO: I didn't know it was gonna be a hit Mike -- I swear to god I didn't know it was going to be a hit. JOHNNY OLA bumped into me in Beverly Hills -- and he said that he wanted to talk -- he said that you and -- and -- ROTH were in on a -- a -- big deal together. And that there was something in it for me if I'd help 'em out. He said that -- he said that -- you were bein' tough on the negotiations. But if they could get a little help -- and close the deal fast -- it'd be good for the family.