An exasperated Rwandan witness and a frustrated defence lawyer exchanged testy words Wednesday as Canadian legal standards and uncertain Rwandan recollections clashed at a groundbreaking war crimes trial.

A Rwandan witness known as C17 peppered her answers with sarcastic notes as she was grilled by defence lawyer Richard Perras over her experience in the Rwandan genocide of 1994.

The witness has testified that Perras's client, former Toronto resident Désiré Munyaneza, raped her four times during the Rwandan killing spree.

When Perras asked the witness to compare her height to Munyaneza, she answered she didn't have a measuring stick when he raped her.

When the defence lawyer asked her about the clothing worn by Hutu militias running the massacre of her Tutsi countrymen, C17 answered that the men "certainly weren't naked."

When Perras pointed out the woman couldn't identify the 40-year-old Munyaneza for RCMP officers in a photo lineup in 2005, she denied it.

"It's a lie," she declared.

A few minutes later, Quebec Superior Court Justice André Denis warned Perras to keep a civil tone and turned to the witness who was testifying behind a screen to hide her identity from onlookers.

"Don't see the lawyer as an enemy," Denis said. "He is only doing his job."

Munyaneza faces seven charges including genocide and crimes against humanity in Canada's first trial under the Crimes Against Humanity and War Crimes Act, enacted in 2000. If convicted, Munyaneza faces a life sentence in a Canadian prison without parole for 25 years.

C17 has testified for two days about several weeks starting in April 1994, when most of her family was wiped out and she was beaten and raped repeatedly. She was then 20.

In a soft voice speaking Rwanda's national language, Kinyarwanda, the woman described through translators how she spent weeks being shuttled or running from one horrific massacre scene to another.

She watched a dozen family members being killed, including her mother.

The woman described fleeing with other half-naked refugees from a site where dozens of Tutsis were being killed.

"It was quite embarrassing," she said. "Some were wearing petticoats, some were without anything with their breasts showing. It was humiliating."

The woman said she finally ended up a sex slave for Hutu militia members camped out at a local government office near the town of Butare. There she was attacked by Munyaneza, she said.

The witness and others say they saw Munyaneza hack several people to death during the Rwandan bloodbath that killed at least a 500,000 Tutsis.

Munyaneza claimed refugee status in Canada in 1997 and was arrested in Toronto in 2005.

C17 seemed to lose her temper as Perras pressed her for the number of times she saw one accused war criminal who she said was frequently in the company of Munyaneza.

Her delicate quiet voice swelled, sending a buzz over the loudspeaker system meant to amplify her words. She suggested Perras should read her testimony from a war crimes tribunal held in Arusha, Tanzania, in 2001. She said she was sick for four months after that experience.

"They caused me some unspeakable wounds," she said. "I would like them to show you the testimony I gave in Arusha and then you will understand." 

C17 is among 12 Rwandan witnesses expected to testify at Munyaneza's trial. The trial before a judge alone is scheduled to last into the summer.