C.R.S. § 18-1-604

(1) Unless otherwise provided by the statute defining the offense, a person shall not be legally accountable for behavior of another constituting an offense if he is a victim of that offense or the offense is so defined that his conduct is inevitably incidental to its commission. (2) It shall be an affirmative defense to a charge under section 18-1-603 if, prior to the commission of the offense, the defendant terminated his effort to promote or facilitate its commission and either gave timely warning to law enforcement authorities or gave timely warning to the intended victim.