Board Thread:Versus Debates/@comment-37960523-20190522205733/@comment-4961229-20190528222335

But he can damn sure kill Sasuke, whom he was attempting to capture alive, because he needed a live Uchiha to experiment on. Kabuto says out of his own mouth: "Protecting Sasuke with your Susanoo slowed you down. Please, I would never hurt Sasuke. He's my precious test subject." Now, if all bets are off, Sasuke can simply be disposed of. Once Sasuke's out of the picture, Itachi has no defense against Kabuto's Demonic Flute Genjutsu.

Sasuke's and Itachi's Sharingans were each other's counter to sound based genjutsu. Without one another they have no counter. Itachi can be immobilized with sound based genjutsu and get his body wrecked as Kabuto was able to do even with Sasuke there a few times. Kabuto can then rewrite his tag or web up his remains in Kidōmaru's cocoon for safe keeping until later. If Edo Itachi's body is not allowed to repair itself he's stuck.