It was my understanding that it was the Kahanes, and those rather nasty folks that killed Rabin, or had him killed.
Even the extreme left in Israel doesn't claim that The Kahanes were behind the killing of Robin. Please provide one link that anyone claims such a thing.
Binyamin Zeev Kahane was murdered by Palestinian terrorists. OU in the 2 links you provided is asking people to send condolences to his family because he was murdered. Has nothing to do with the murder of Robin.
If you cannot provide a link, I would strongly urge you to retract your statements about OU and the Kahane family.