Colo. Rev. Stat. § 13-25-139
When a party to a criminal case wrongfully procures the unavailability of a witness, a statement otherwise not admissible pursuant to the Colorado rules of evidence that is offered against the party that was involved in or responsible for the wrongdoing that was intended to, and did, deprive the criminal justice system of evidence is admissible as an exception to the hearsay rule; except that such a statement is not admissible unless the proponent has given to the adverse party advance written notice of an intention to introduce the statement sufficient to provide the adverse party a fair opportunity to contest the admissibility of the statement. In determining the admissibility of the evidence, the court shall determine, prior to the trial, whether the forfeiture by wrongdoing occurred by a preponderance of the evidence.
C.R.S. § 13-25-139