Yugoslav war crimes tribunal judge Patrick Robinson said burning at least 119 Muslims to death in the eastern Bosnian town of Visegrad "exemplified the worst acts of inhumanity that one person may inflict on others."
He sentenced Milan Lukic to life in prison and Sredoje Lukic to 30 years.
Robinson said Milan Lukic was the ringleader in both incidents, helping herd victims into the houses, setting the fires and shooting those who tried to flee the flames. The judgment said his cousin Sredoje Lukic aided and abetted in one of the blazes
Witnesses "vividly remembered the terrible screams of the people in the house," Robinson said, adding that Milan Lukic used the butt of his rifle to herd people into the house, and said, "come on, let's get as many people inside as possible."
Milan Lukic shook his head but looked unmoved as Robinson pronounced sentence. Sredoje Lukic leaned back in his chair, his face blank.
Even Robinson, a veteran judge at the tribunal that has been prosecuting Balkan war crimes for 15 years, sounded stunned by the Visegrad atrocities.
"The perpetration by Milan Lukic and Sredoje Lukic of crimes in this case is characterized by a callous and vicious disregard for human life," he said.
"In the all-too-long, sad and wretched history of man's inhumanity to man, the Pionirska street and Bikavac fires must rank high," the judge said.
Prosecutors seeking to clear the court's docket as quickly as possible had asked for the Visegrad case to be handed to a Bosnian court because the cousins were relatively low-ranking suspects. But tribunal judges refused, saying the allegations were so serious they should be handled in The Hague.
They welcomed Monday's verdicts, which can still be appealed by the cousins.
"The prosecutor is satisfied with this decision because it reflects the gravity of the crimes committed and the responsibility of the accused," spokeswoman Olga Karvan said. "The prosecutor would particularly like to acknowledge the courage demonstrated by the victims who came forward in this case and presented their evidence in court."
Milan Lukic also was convicted of murdering 12 other Muslims, shooting them in the back on the banks of the Drina River, which runs through Visegrad, so the current would sweep away their bodies. One of the victims was murdered in front of his wife and child.
Two men survived the summary executions by playing dead, and testified about their ordeal.
Robinson said Milan Lukic "ignored the victims' pleas for their lives," as he and other Serb paramilitaries executed them with a single shot in the back before firing into the bodies of any men they believed were still alive.
Milan Lukic led a paramilitary group known as both the "White Eagles" and the "Avengers," which terrorized Muslims in Visegrad. His cousin Sredoje was a local policeman and a member of the group.
Both men also were convicted of cruelty for visiting a detention center to savagely beat Muslim inmates.
Milan Lukic was arrested in August 2005 in Argentina and sent for trial in The Hague. His cousin surrendered to Bosnian Serb authorities and was transferred to The Hague a few weeks later.