Quote Originally Posted by UChessmaster View Post
Kabuto didn`t released it because then every other zombie would be released as well.
He can summon and pack up individual zombies he has summoned. The summoning of people is on an individual level and is not linked to the rest of the group. There is nothing to suggest there is 'system shutdown' command in Edo Tensei.

He lost control of Itachi, which is why he was eager to put that tag in his head.