I. A person is guilty of an attempt to commit a crime if, with a purpose that a crime be committed, he does or omits to do anything which, under the circumstances as he believes them to be, is an act or omission constituting a substantial step toward the commission of the crime.
II. As used in this section, "substantial step" means conduct that is strongly corroborative of the actor's criminal purpose.
III. (a) It is an affirmative defense to prosecution under this section that the actor voluntarily renounces his criminal purpose by abandoning his effort to commit the crime or otherwise preventing its commission under circumstances manifesting a complete withdrawal of his criminal purpose.
(b) A renunciation is not "voluntary" if it is substantially motivated by circumstances the defendant was not aware of at the inception of his conduct which increase the probability of his detection or which make more difficult the commission of the crime. Renunciation is not complete if the purpose is to postpone the criminal conduct until a more advantageous time or to transfer the criminal effort to another but similar objective or victim.
IV. The penalty for attempt is the same as that authorized for the crime that was attempted, except that in the case of attempt to commit murder the punishment shall be imprisonment for life or such other term as the court shall order.