(a) A person is guilty of an attempt to commit a crime if:
(i) With the intent to commit the crime, he does any act which is a substantial step towards commission of the crime. A "substantial step" is conduct which is strongly corroborative of the firmness of the person's intention to complete the commission of the crime; or (ii) He intentionally engages in conduct which would constitute the crime had the attendant circumstances been as the person believes them to be.
(b) A person is not liable under this section if, under circumstances manifesting a voluntary and complete renunciation of his criminal intention, he avoided the commission of the crime attempted by abandoning his criminal effort. Within the meaning of this subsection, renunciation of criminal purpose is not voluntary if it is motivated, in whole or in part, by circumstances, not present or apparent at the inception of the person's course of conduct, which increase the probability of detection or apprehension or which make more difficult the accomplishment of the criminal intention. Renunciation is not complete if it is motivated by a decision to postpone the criminal conduct until a more advantageous time or to transfer the criminal effort to another but similar objective or victim.