Men on the ship seized off the coast of British Columbia wave to a helicopter. Government investigators are trying to determine if some of the men pose a risk to security. (RCMP)

Authorities investigating the 76 migrants aboard a ship seized off Vancouver Island told an immigration hearing Monday that two items of clothing the men brought with them tested positive for explosive residue.

Investigators also say there had been an attempt to disguise the ship's identity and that the vessel actually belongs to the Tamil Tigers, an alleged terrorist organization banned by the federal government.

The ship carrying the men was seized Oct. 17 after Australian intelligence officials apparently tipped off Canadian authorities about its impending arrival.

Only one of the 76 migrants, believed to be a minor, has been released. The 75 others remain in custody in Vancouver while authorities try to establish whether they are a security risk to Canada.

Lawyers for the men said they are refugees who were on the losing side in the long Sri Lankan civil war, and who were escaping persecution in their homeland.

Allegedly used by rebels

The two clothing items, which were not identified, tested positive for explosives residue from pentaerythritol tetranitrate, or PETN, and TNT. Lawyers for the men said that PETN is also used in heart medication.

When the ship was seized, it bore the name Ocean Lady, but investigators say that the vessel is actually the Princess Easwary, owned by the Tamil Tigers and once used to transport arms for the Tamil rebels in Sri Lanka.

A transponder that was found aboard was not turned on because it would have revealed the ship's real identity, investigators said.

The federal government has detained the new arrivals because their identity has been difficult to establish with certainty, although the men did carry identification papers.

The government has relied on information provided by Rohan Gunaratna, head of a Singapore-based think tank called the International Centre for Political Violence and Terrorism Research.

Gunaratna's impartiality has been questioned by defence lawyers.

One of the migrants has been found to be the subject of an Interpol arrest warrant prompted by his membership in the Tamil Tigers.

Investigators are trying to determine if the other men have similar connections.

It will be up to an immigration adjudicator to assess whether the new evidence that has surfaced is sufficient to hold the men on security grounds.