Wasn't Renda his brother in law? I don't think he would have been brave or dumb enough to stage a fake kidnapping to try and take over.

I think he was kidnapped and tortured for info, info to what who knows? Maybe they were trying to get into Rizzuto's hidden money? Maybe they were trying to shake him down before killing him. I think money was the issue here, and someone was trying to get it.

Consigliere or Underboss it doesn't matter to me, he was pretty high up when he was killed.