After a trial that opened new avenues for bringing war criminals to justice, a Belgian court today sentenced four Rwandans -- two Catholic nuns, a university professor and a businessman -- to prison terms ranging from 12 to 20 years for their role in the 1994 genocide in Rwanda that left at least a half-million people dead.

The four were tried under a 1993 Belgian law giving the country's courts "universal jurisdiction" for crimes against humanity, no matter where they occur in the world. Human rights advocates hope that principle will be applied more broadly to war criminals and others who seek to escape justice by fleeing their home countries, as the four defendants did.

All four maintained their innocence throughout the eight-week trial. In brief remarks before the jurors retired to decide the sentences, each briefly expressed confidence in the justice system. Only one, Sister Maria Kisito, went further, calling the testimony against her "a lie."

Hours before the sentencing, the same jury convicted the four of murder and involvement in the genocide, in which members of the country's Hutu tribe set upon the rival Tutsi tribe in a mass slaughter. All four defendants are Hutus.

The trial also marked the first time that any Rwandan has faced a jury trial for the mass slaughter. A military tribunal in Switzerland had previously convicted a Rwandan of similar charges.

Far from bringing some measure of closure to the Rwandan genocide, today's verdict and sentences -- and the reactions among the Rwandans who crowded into the courtroom -- in many ways served to underscore the deep tribal division that makes reconciliation in Rwanda impossible for now. Even the courtroom was divided, with Hutus, who came to show sympathy for the defendants, seated on one side and Tutsis on the other.

Sister Maria Kisito, who received 12 years, and her Mother Superior, Sister Gertrude, who received 15 years, were convicted of aiding in the slaughter of some 7,000 people who sought refuge at their convent in southern Rwanda. Prosecutors argued that they called in Hutu militiamen to drive people out of the convent knowing they would be killed, and later provided gasoline that militiamen used to set fire to a garage in which about 500 Tutsis had taken refuge.

Their defense lawyers argued that they were innocent bystanders who believed the violence had ended and that the refugees would not be harmed on leaving the convent.

Both of the Benedictine nuns wore their brown-and-beige habits during the trial, and their presence in the courtroom revived embarrassing questions for the Vatican about the culpability of Hutu clergy in assisting the slaughter.

The convicted professor, Vincent Ntezimana, was ordered jailed for 12 years for providing militia murderers with the names of colleagues. The businessman, Alphonse Higaniro, was described in testimony as a Hutu extremist who helped plan and instigate killings in the Butare region.

All four fled to Belgium after a Tutsi-led rebel army took over the country and ended the attacks.

They were free throughout the trial, but after the sentences were read, the chief prosecutor asked that they be immediately jailed. They were convicted in Belgium's top criminal court, meaning they can only appeal legal technicalities, not the facts of the case. Their lawyers said today it was too early to decide their next step.

For many Rwandans, the verdicts raised the nagging question of when the masterminds of one of the century's worst genocides will finally face justice.

There have been a handful of convictions by an international tribunal in Arusha, Tanzania, but so far they have been of relatively low-level figures.

"It's sad. It's sad, but it's right," said Alison DesForges, a consultant with Human Rights Watch who has been following Rwanda for years and was an expert witness at the trial. "The tragedy is that it's easy to convict nuns -- but when are we ever going to get the people who were the brains behind it?"

"It's justice. But it's just the beginning," said Eugenia Kangabire, a Rwandan Tutsi living in Belgium who attended the trial. "We hope you do something in the United States. There are so many Rwandan refugees in the United States who committed crimes."

More trials are likely in Belgium. A lawyer attending today's session said he represents the family members of three Belgian aid workers killed when the genocide began in April 1994, and that they have identified some of the culprits. Also, he said, the killers of 10 Belgian peacekeepers could also be brought to trial.

Yet having this trial in Belgium, Rwanda's former colonial ruler, was offensive to some Hutus. They said that a trial in which an all-white, European jury judged four Africans for events that happened in Africa seemed out of context, and they questioned why there was no trial of European government officials to ascertain their knowledge of, or complicity in, what happened in Rwanda in 1994.

One Rwandan man, a Hutu who fled to the country now known as Congo following the massacres, said he found it odd the nuns were accused of not trying to prevent the attacks on Tutsis sheltering in their convent, when Belgian peacekeeping troops there at the time also did not intervene to stop the slaughter. "Quite frankly, this is a totally political process," said Jean-Claude Niwenshuti, 25.

Mike Gantna, 32, a Rwandan Tutsi, raised historical issues. "What about the French and the Belgians?" he asked. "They are the ones who brought tribalism between the Hutus and the Tutsis. They brought colonialism. They have to put themselves on trial."

Sister Gertrude, left, and Sister Maria Kisito were convicted of aiding in the slaughter of 7,000 people who sought refuge at their convent in Rwanda.