He said he saw her actively strangling one of the babies on the baby monitor.
I think the defence will rely on this.
3.4 – Self-defense /
defense of another
Under Colorado law, self-defense is not an affirmative defense in itself to first-degree murder charges. However, it may negate the element of extreme indifference required to sustain them.
Likewise, showing that you were acting to defend someone else is strong evidence that you did not kill someone with an extreme indifference to the value of human life generally.
Colorado "first degree murder" laws |18-3-102 C.R.S.