Generally speaking, prior bad acts of someone cannot be used to show conformity with current alleged bad behavior. However, Colorado case law is clear that prosecutors can use prior incidents of alleged domestic violence in an effort to show a pattern. They would, however, have to go through a hearing in which a court would need to determine the admissibility (essentially, would the prejudice outweigh the probative value). Probably the biggest issue here would be that there are two different victims (thus making the pattern argument harder). This process is the only way that the prior incident can be brought in...the DA unfortunately cannot just bring it into evidence without filing the motion and winning the hearing.