Could you share where you found that info? It's actually been rather difficult to find a comparison of murder sentencing for CO juvenile v adult court, especially since so many juveniles are charged as adults for the crime.
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That being said, if the claim is that they should be charged as adults because the sentencing for juveniles is too light, it seems the better way to address that would be to increase the sentence in juvenile court, not to claim that the accused is something they're not.