MADISON, Wis. — A state law that makes false bomb threats a crime does not infringe on free speech, an appeals court ruled yesterday.

Milwaukee County Circuit Court Judge Mary Triggiano had declared the law unconstitutional, ruling it banned speech protected by the First Amendment. But the District 1 Court of Appeals overturned that decision, agreeing with prosecutors that the law is constitutional.

The law says anyone who knowingly gives false information concerning an attempt to destroy property by explosives is guilty of a felony.

Yesterday's ruling was the first time a state appeals court had considered the 4-year-old law. "This is an important decision because it does not prevent the enforcement of ... the 'bomb scares' law, which is directed at very real threats to public safety," Wisconsin Department of Justice spokesman Kevin St. John said.

The case in question involved a student identified in court documents as Robert T. who called police from a pay phone at Washington High School in Milwaukee to claim falsely that there was a bomb in the school. Police responded by going to the school. The student was caught making the 2006 call on a surveillance camera and admitted he did so because "he was bored and was looking for something to do."

Prosecutors sought a petition for delinquency in juvenile court against him. But Triggiano dismissed the case, agreeing with Robert T.'s attorney that the law banned too much speech to be constitutional. Prosecutors appealed.

The appeals court ruled the law is constitutional because it bans only "true threats," which are not protected speech. Previous court rulings have defined such threats as statements that could reasonably be interpreted as serious expressions and not hyperbole or sarcasm. "Here, the police who responded to Robert T.'s phone call believed the threat was real," Judge Patricia Curley wrote for the three-judge panel. "Also, Robert T. apparently intended to frighten the listener; thus, his call appears to fall within the ambit of a 'true threat.' Therefore, the statute is constitutional."

She also rejected Robert T.'s attorney's argument that a 2003 U.S. Supreme Court decision, Virginia v. Black, narrowed the definition of true threats to those that threaten bodily harm or death to a person or a group of people. In that case, the court upheld a Virginia law that banned cross-burning.

Many prosecutors have convicted people who threatened to blow up property or made false threats since then and those prosecutions have not been challenged, the court said. "We are satisfied that Robert T.'s interpretation is wrong," Curley wrote in reinstating the case.