Board Thread:General Discussion/@comment-2211792-20130814091737/@comment-8986886-20130816135018

Nova Alexandria wrote: He than took Souken back while he was still alive, and experimented him to death.

The problem with this theory, since Quincy Souls can't willingly leave their bodies, is that Mayuri would need some kind of energy conversion machine, like the one Kisuke used to allow Uryü to enter Soul Society as a Soul.