Why do the resurrected bodies disappear in the impure world resurrection jutsu?


Some of the resurrected people like Sai's brother were freed from the jutsu
although Kabuto told Tobi that the resurrected people can't be killed. This is
a pic of a conversation between Kabuto and Tobi.

[![enter image description
here](https://i.stack.imgur.com/nMg7g.jpg)](https://i.stack.imgur.com/nMg7g.jpg)

Similarly, Sasori also disappeared after telling Kankuro to use his puppet
parents.

[![enter image description
here](https://i.stack.imgur.com/DZN1V.jpg)](https://i.stack.imgur.com/DZN1V.jpg)

How can the souls be freed from the bodies even if the user who resurrected
them did not release them? And why didn't this happen when the third hokage
was fighting his predecessors during the chunin exams?




The souls can be freed from the[ Impure World
Reincarnation](http://naruto.wikia.com/wiki/Summoning:_Impure_World_Reincarnation)
if they are given closure. Experiencing a emotional change allows them to
break out of the jutsu and the soul can ascend.

Orochimaru
[stated](http://naruto.wikia.com/wiki/Summoning:_Impure_World_Reincarnation)
that Hashirama Senju could break the summoning jutsu if he wanted. I'm not
sure why he chose not to during the fight with Hiruzen Sarutobi.

