In the summer of 1990, the mutilated bodies of two teenage boys and two slightly older adult friends--all of whom had been living on the streets of Guatemala City--were discovered in an overgrown field on the outskirts of the Guatemalan capital. In addition to the mutilation, a boiling liquid had been poured over one of the victims. All had been shot in the head.

Witnesses who saw the street boys abducted from a downtown parking lot days earlier would later implicate a pair of Guatemalan police officers in those killings, as well in the killing of another 17-year-old.

The Guatemalan courts eventually cleared the officers of wrongdoing, prompting complaints from human rights activists and the victims' families that critical testimony and evidence had been unfairly ruled inadmissible, and that the investigation had been inadequate and marred by a cover up.

But on Friday, an international court based in San Jose released a ruling that there is sufficient evidence that the police carried out the killings, and that the government of Guatemala failed to protect the rights of the victims and provide them justice, as required under international law.

The unanimous ruling by a seven-judge panel of the Inter-American Court on Human Rights, a judicial arm of the Organization of American States, was the first case involving violations of the human rights of minors to have gone before the court in its 20-year history.

The court concluded that Guatemala had violated seven articles of the American Convention on Human Rights, including those that affirm a person's right to life and access to effective and impartial justice. Guatemala was also cited for violating sections of the Inter-American Convention for the Prevention and Punishment of Torture.

Human rights activists said they hoped the ruling would send a strong message to authorities and other groups that for decades have targeted and abused street children deemed to be public nuisances. Experts estimate that 40 million children live and work on the streets throughout Latin America, and that about 100 million do worldwide. In Guatemala and elsewhere, children's advocates say, minors are often victims in officially sanctioned killing sprees against street people.

Guatemala, one of 20 countries that recognizes the jurisdiction of the Inter-American court, will now be required to investigate, prosecute and punish those responsible for the crimes and any miscarriage of justice, including judges who might have acted negligently or dishonestly. Officials said that while follow-up convictions by governments in such cases are rare, monetary damages have usually been paid to the victims' families.

The minors allegedly killed by police were Julio Roberto Caal Sandoval, 15; Jovito Josue Juarez Cifuentes, 17; and Anstraun Villagran, 17. Of the two officers tried for the deaths, one, Samuel Rocael Valdes, reportedly fled after the trial, while the other, Nestor Fonseca, has died.

Guatemalan officials argued before the court that the state did not have the authority to overturn the decision of the country's Supreme Court, which had upheld a lower court ruling that the accused officers were not guilty in the deaths and torture of the victims. In their closing arguments here, Guatemalan representatives said the case should be thrown out based in part on that constitutional separation of powers.

Covenant House Latin America, an outreach organization for street children that filed the original complaint in the case, has six other complaints relating to alleged abuses of street children in Guatemala, and four others against Honduras, pending before the Inter-American Commission on Human Rights.