Unless otherwise provided by the statute defining the offense, a person shall not be legally accountable for behavior of another constituting a criminal offense if:
(1) He is a victim of that offense; or
(2) The offense is so defined that his conduct is inevitably incidental to its commission; or
(3) Prior to the commission of the offense, he voluntarily terminated his effort to promote or assist its commission and either gave timely and adequate warning to law enforcement authorities, or to the intended victim, or wholly deprived his complicity of its effectiveness in the commission of the offense. The burden of injecting this issue is on the defendant, but this does not shift the burden of proof.