MONTREAL - A retired tobacco executive says he can't remember the details of research documents that were destroyed under his watch and can't recall why they might have been shredded.

Roger Ackman, 73, was part of a management team that destroyed documents that included industry research related to the health effects of smoking, but he told a historic civil trial Tuesday that his recollection of the events is hazy.

Ackman was testifying in a landmark case pitting Quebec smokers against Canada's three largest tobacco companies over $27 billion in damages.

Separate groups of claimants are arguing that they were either misled by cigarette companies about the addictiveness and dangers of smoking, or that they personally suffered health problems for which the industry is to blame.

Ackman repeatedly cited memory gaps as the plaintiffs' lawyers went through a handful of confidential tobacco company documents, which specifically mention the health effects of smoking and which were purportedly destroyed in Montreal.

One document Ackman was questioned on included a study, from March 1974, that revealed testing on hamsters cited tobacco smoke as a "tumour promoter." Another study from 1973 pointed to emphysema of the lungs as being linked to cigarette smoking.

Ackman claimed to have never seen either document and said neither one was a topic of discussion among Imperial's braintrust.

The documents were destroyed in Canadian offices in the early 1990s -- an unprecedented move, according to Ackman's testimony.

The original documents were tracked down at British American Tobacco offices in England a few years ago. Their existence came to light in a U.S. trial. Lawyers for the plaintiffs have said they'd never have known about them if not for the American proceedings.

"I have no present recollection, sir," repeatedly said Ackman, a former vice-president of legal affairs at Imperial Tobacco, under questioning from the plaintiffs' lawyer Gordon Kugler about various policies and memorandums. Some of the documents were signed by him.

When asked if some of the information in the documents linking smoking to illness would have been of interest to government scientists, Ackman replied: "I have no opinion."

It was a U.S. court that concluded in 2006 that much of the research was destroyed in the United States, Canada and Australia and transferred to Britain to hide evidence and create hurdles for gathering evidence.

In 2006, the U.S. Federal District Court concluded tobacco companies had set up a complex series of hurdles to downplay research on the dangers of smoking, ranging from public relations spin to the shredding of documents.

The ruling by U.S. Judge Gladys Kessler said research was shredded in Canada, the United States and Australia. Some copies have remained on file with British American Tobacco.

One of a series of internal memos and letters deposited Tuesday showed that Imperial Tobacco revised its policies in the early 1990s and agreed to shred or return pertinent research information as requested by British American Tobacco.

Ackman continues on the stand Wednesday in what is considered the largest class-action suit in Canadian history and the first trial of its kind involving cigarette companies in this country.

The trial, which got under way in early March, is expected to last as long as two years.