Canadian police were warned of a plot to blow up an airliner months before 329 people were killed in a bombing in 1985, a public inquiry has heard.
Air India flight 182 plunged into the Atlantic Ocean near Ireland
An unidentified witness said he had been approached by the plotters to help plant a bomb on an aircraft.
Air India Flight 182 blew up off the Irish coast on its way from Canada to India, killing everyone on board.
A criminal trial sentenced one suspect to five years. The inquiry is now looking at how the case was handled.
Two other suspects were acquitted in 2005 after one of the longest and most expensive trials in Canadian history.
The witness, speaking from behind a curtain, told the inquiry that Sikh separatists in Vancouver had offered him $180,000 (£90,000) to help them get a bomb on an aircraft.
He said he had gone to police instead of helping the plotters.
A former Vancouver policeman also said he had been told about the plot in 1984 by an informant and that he had passed the information on to the Canadian Security Intelligence Service (CSIS).
Canadian officials have said that warnings they received before the bombing were not specific to any particular date, airline or flight.
The bomb was attributed to Sikh militants seeking revenge against the Indian government for the 1984 storming by government troops of the Golden Temple in Amritsar, India.
The public inquiry was set up after pressure on the government from relatives of victims who said that Canadian police could have prevented the attack and then bungled the investigation.
The inquiry, in Canada's capital Ottawa, cannot revisit the verdicts of the criminal trial.