(1) In any prosecution for criminal solicitation or criminal conspiracy in which the crime solicited or the crime contemplated by the conspiracy was not in fact committed, it is a defense that, under circumstances manifesting a voluntary and complete renunciation of his criminal purpose, the defendant prevented the commission of the crime.
(2) A renunciation is not "voluntary and complete" within the meaning of this section when it is motivated in whole or in part by:
(a) A belief that circumstances exist which pose a particular threat of apprehension or detection of the accused or another participant in the criminal enterprise or which render more difficult the accomplishment of the criminal purpose; or (b) A decision to postpone the criminal conduct until another time or to transfer the criminal effort to another victim or another but similar object.