Vincent Santillanes was convicted of child abuse under a statute that he believes is unconstitutional because it criminalizes ordinary civil negligence. The Supreme Court of New Mexico reviewed his case and found that the trial court made an error by instructing the jury on a civil negligence standard instead of a criminal negligence standard. The defendant argued that the term "negligently" in the statute should be read to mean criminal negligence or deemed unconstitutionally vague or overbroad. The court found that the trial court's refusal to give the requested jury instruction defining negligence as criminal negligence was an error. The Court of Appeals erred in its interpretation of the relevant rule and the defendant did preserve his issue for appeal. The court must determine the requirement of criminal negligence. The defendant argues that giving felony status to acts of civil negligence violates substantive due process, while the State argues that the civil negligence standard has been long-standing and there is no reason to change it. The trial court's instruction on both intentional and negligent child abuse was incorrect, and the conviction by general verdict must be overturned because the trial court instructed the jury on the wrong standard of negligence.

This case involves determining the level of negligence required when the mens rea element is included in a criminal statute but left undefined, such as the term "negligently" in a child abuse statute. Previous case law has consistently applied a civil negligence standard in the child abuse statute, but a higher standard than tort negligence should be applied when the crime is punishable as a felony. The child abuse statute is not unconstitutional, but rather a matter of judicial interpretation. Criminal statutes must be strictly construed and defined with appropriate definiteness, and any doubts must be resolved in favor of lenity.

The court interprets the mens rea element of negligence in the child abuse statute to require criminal negligence. The trial court erred by not instructing the jury on a criminal negligence standard, but the error was not reversible because the evidence presented satisfies the standard of criminal negligence. The court must decide whether the new interpretation of "negligently" in the child abuse statute should apply retroactively or only to future cases. Applying the criminal negligence standard retroactively would unduly burden the criminal justice system and should be applied prospectively.

The court ruled that the criminal negligence standard in the child abuse statute should only be applied prospectively to prevent unfairness. The court is interpreting the statute, not defining the crime of negligent child abuse. The civil negligence standard goes beyond the statute's intended scope and criminalizes innocent conduct. The court overrules inconsistent opinions and affirms the defendant's conviction. The criminal negligence standard adopted by the court will apply to all pending cases.