Ten years since their last encounter, the former Canadian general in charge of UN peacekeeping forces in Rwanda during the 1994 massacre arrived in court to testify against the former army colonel he says is responsible.

In his first day of testimony in Arusha, Tanzania, retired Lt.-Gen. Romeo Dallaire clearly remembered the last time he met former Rwandan Army Colonel Theoneste Bagosora.

"It was a very confrontational meeting," Dallaire said. "Colonel Bagosora threatened me with his pistol, and was told that the next time he met me he would kill me."

Dallaire is considered a star witness for the prosecution against Bagosora and three of his fellow officers -- Anatole Nsengiyumva, Aloys Ntabakuze, and Gratien Kabiligi.

All four have all pleaded not guilty to charges of genocide and crimes against humanity.

In his first day of testimony for the prosecution, Dallaire described the man he says was architect of a campaign to exterminate the Tutsis, as someone apparently comfortable with the violence swirling around him.

"What I found incredible to witness was I had never found someone so calm and so at ease with what was going on," Dallaire told the tribunal.

"He shuffled some papers and signed some documents," he continued, describing his encounter with the former Rwandan colonel. "It was like they were totally on another planet, or something was going as to plan."

Bagosora accused of ethnic genocide

Bagosora is accused of planning the mass killings of Tutsi rebels, despite concessions made by his Hutu government for peace.

Prosecutors say he seized control of the country after President Juvenal Habyarimana was killed when his plane was shot down on April 6, 1994. The genocide began hours later at roadblocks set up in the capital city, Kigali.

Dallaire was in charge of UN forces in Rwanda between October 1993 and August 1994.

The former Canadian general made several appeals to the UN for help, saying he had heard from an informant that preparations were being made for massacres. He was repeatedly told not to get involved.

Dallaire's force of 2,519 soldiers also lost a key component -- 450 Belgian troops -- after 10 Belgian soldiers were killed by Hutus.

Even as the killing raged in Rwanda, the UN passed a resolution April 16 reducing the UN force to a staff of 270 troops. It wasn't until May 16 that it approved the deployment of 5,000 troops.

By then, more than 500,000 people, mostly minority Tutsis and politically moderate Hutus, had been killed in a massacre orchestrated by the governing Hutu extremists.

An official UN inquiry in 1999 showed that if Dallaire had been allowed to act in the early moments of the massacre, the killings could be have been slowed, or even prevented.

Adding to the high death toll was the fact many Rwandans stayed in their homes, believing they were safe because there were peacekeepers in the country.

Dallaire's emotional scars

Though his determination earned him praise as a hero of sorts, the horrors Dallaire witnessed in Rwanda left him with severe emotional trauma.

Upon returning home from the Rwanda mission he attempted suicide. Then, in April 2000 he retired because of severe post-traumatic stress. Dallaire details the shocking events, and his personal journey, in the book "Shake Hands with the Devil."

It's enough to have the defence already hinting that such a distraught individual can't possibly make a reliable witness.

Tribunal defense lawyer Jean Yaovi Degli told CTV News that his team may be aiming to expose serious gaps in the former UN commander's memory.

"Some people saw something small and suddenly it becomes big. Some people saw nothing and now they claim they saw everything," he told CTV reporter Murray Oliver, hinting at the defence strategy.

In 1998, Dallaire testified at the trial of Jean-Paul Akayesu. The former mayor of Taba in central Rwanda was subsequently convicted of genocide and sentenced to life in prison.

The trial of the four former Rwanda officers began in April 2002.

The prosecution is expected to keep Dallaire on the stand until Wednesday, at least. Then, the defense lawyers will have their turn.