Michael Martinez (defendant) was 19 years old when he had sexual intercourse with a 15-year-old girl. The State of Utah (plaintiff) charged Martinez with unlawful sexual activity with a minor, a felony. Prior to trial, Martinez moved to admit evidence in support of an affirmative defense that the victim represented herself to be 17 years old at the time of the sexual intercourse. Martinez claimed the state law did not impose strict liability for the crime. The trial court denied Martinez’s motion. A jury convicted Martinez, and he appealed. The court of appeals affirmed, holding that the legislature intended the state law to impose strict liability and expressly precluded the defense of mistake as to the victim’s age. The Supreme Court of Utah granted certiorari.