MADISON, Wis. - Fourteen-year-olds convicted of homicide can be sent to prison for life without parole, the Wisconsin Supreme Court ruled Friday in upholding a life sentence for a man who was that age when he helped throw a boy off a parking ramp to his death.

In a case watched by psychiatrists and family advocates, the court found that neither the U.S. nor the Wisconsin Constitution prohibited life sentences without parole for 14-year-olds in homicide cases and that no national consensus had formed against such sentences.

"Contemporary society views the punishment as proportionate to the offense," Justice Annette Kingsland Ziegler wrote for the majority.

Omer Ninham was convicted of first-degree intentional homicide for his role in the death of 13-year-old Zong Vang in Green Bay in 1998. Ninham was 14 at the time. A judge sentenced him to life without parole two years later, when Ninham was 16.

Ninham's attorney, Byron Stevenson of the Equal Justice Initiative, argued that the sentence amounted to cruel and unusual punishment. He vowed to appeal to the U.S. Supreme Court.

"I absolutely believe it's just a matter of time before states are going to have to reevaluate the judgment that you can punish [a juvenile] the same way you can punish an adult," he said.

The Wisconsin Psychiatric Association and the Wisconsin Psychological Association were among groups that filed informational briefs in the case.

The U.S. Supreme Court in 2005 ruled that sentencing juveniles to death is unconstitutional. Last year it ruled that life with no parole for anything less than homicide was unconstitutional as well.

Groups such as the American Civil Liberties Union have been fighting for reviews of youth life sentences in major crimes since the 2005 ruling. They argue that those constitutional prohibitions should extend to homicide cases as well.

The Wisconsin justices said in their 5-2 decision that Ninham failed to show that children 14 and younger deserve different constitutional status in homicide cases.

In Ninham's case, the punishment fit a crime that "cannot adequately be reduced into words," the opinion said.

Ninham and four others ages 13 to 14 accosted Vang as he rode his bike home from a grocery with a bag of tomatoes for his family.

Vang ran into a nearby hospital parking ramp, where the group cornered him on the top floor. There, Ninham and a friend seized Vang by the wrists and ankles. As Vang cried and screamed, they threw him over the edge. He fell five stories to his death.