The role racism played during the Kanishka bombing investigations, which have been dragging on since more than two decades without a significant result, has been the dominant issue at the Air India inquiry commission hearing even as the Canadian government termed the allegations as baseless.

Sociologist Sherene Razack, professor at the University of Toronto, was grilled about a report she prepared for the victims' families alleging that systemic racism led to Canadian officials minimising the warnings to Air India and being slow to respond after the devastating bombing.

The hearings led by former Supreme Court judge John Major began more than a year and a half ago and are scheduled to wrap up on Friday.

In her testimony, Razack did not level charges of overt racism at individual bureaucrats, politicians or officers but acknowledged that 'there was evidence that some Canadian officials acted heroically.'

An overall structure tainted by systemic racism led people to ignore advance warnings of the attack and hampered the initial probe, she said.

Denying the allegations, Federal government lawyer Barney Brucker said Razack selectively examined a fraction of the evidence and testimony at the inquiry before coming to her unsubstantiated findings.

The question of whether racism played a role in how officials dealt with the 1985 Air India bombing resurfaced on Thursday. At issue was a report commissioned by families of the 329 people killed when Flight 182 en route from Canada [Images] to India exploded off the west coast of Ireland on June 23, 1985.

In her report, Razack argues that a racial bias, perhaps unconscious, affected the government's response to the bombing.

Brucker bristled at the suggestion, saying Razack based the report on selective documents given to her by lawyers of the victims' families.

"You really do nit know what happened in this case, Professor, other than what has been fed to you in these documents," Brucker said during cross-examination.

Razack, who teaches at the University of Toronto's Ontario Institute for Studies in Education, retorted that her remark was a 'particularly contemptuous way of putting it.'

The lawyer went on to note that much of the testimony heard at the inquiry indicates police and security officials did the best they could to head off the bombing.

He also pointed out that former Ontario premier Bob Rae, who oversaw the government's fact-finding mission that led to the inquiry, testified that he found no evidence of racism among key decision-makers.

Razack acknowledged 'people worked very hard' and 'felt very strongly' that they had not discriminated. However, with systemic racism, compassionate people can be trapped in social or bureaucratic structures that produce discriminatory results, she added.

She said Ottawa was slow to recognise the enormity of the tragedy and took more than two decades to call a public inquiry. The downing of the flight was widely blamed on Sikh militants. Only one person -- Inderjit Singh Reyat -- was ever convicted in the plot.

Lawyers for the victims' families are expected to make their closing arguments and offer recommendations for reforming policies.