Arusha, Tanzania ? A former Rwandan army colonel was convicted Thursday of genocide and crimes against humanity for masterminding the killings of more than half a million people in a 100-day slaughter in 1994. Survivors in Rwanda welcomed the watershed moment in a long search for justice.

The U.N. courtroom in Tanzania was packed for the culmination of the trial of Theoneste Bagosora, the highest-ranking Rwandan official to be convicted in the genocide. Onlookers were silent as the 67-year-old was sentenced to life in prison.

“Let him think about what he did for the rest of his life,” said Jean Pierre Sagahutu, 46, in Rwanda, who lost his parents and seven siblings. He escaped by hiding in a septic tank for 2 1/2 months.

Former military commanders Anatole Nsengiyumva and Aloys Ntabakuze also were found guilty of genocide and crimes against humanity and sentenced to life in prison. The former chief of military operations, Brig. Gratien Kabiligi, was cleared of all charges and released.

The U.N. Security Council created a tribunal in 1994 to prosecute those responsible for “genocide and other serious violations of international humanitarian law.”

The 1994 genocide saw government troops, Hutu militia and ordinary villagers spurred on by hate messages broadcast on the radio going from village to village, butchering men, women and children. The consequences still shake the region.

Hutu fighters, chased by the Tutsi military leader who is now Rwanda’s president, fled into Congo at the end of the bloodletting. Rwanda has twice invaded Congo, fueling a conflict that drew in a half-dozen African nations.

Recent clashes in eastern Congo, which borders Rwanda, have driven more than 250,000 people from their homes. Laurent Nkunda, a Congolese Tutsi and former general who quit his country’s army in 2004 to launch a rebellion, contends he is fighting to protect the region’s ethnic Tutsis from Hutu militias.

Perpetrators and victims, meanwhile, struggle to reconcile in Rwanda, a desperately poor and densely packed east African country the size of Vermont.

On Thursday, the court said Bagosora used his position as the highest authority in Rwanda’s Ministry of Defense to direct Hutu soldiers to kill Tutsis and moderate Hutus. According to the indictment against him, Bagosora once said he was returning to Rwanda to “prepare the apocalypse.”

The U.N. and former President Bill Clinton have apologized for failing to intervene. Allegations the international community failed to respond quickly and decisively to crises in Sudan and elsewhere in Africa in subsequent years have been cited as proof the lessons of Rwanda were all too quickly forgotten.

The U.S. called the convictions an important step in providing justice and accountability for the Rwandan people and the international community.