The death of a Montreal man who was zapped by a Taser while in police custody has renewed calls for authorities to stop using the stun gun without more information about their risks.

Quilem Registre, 38, became the second person in less than a week in Canada to die after being subdued with the weapon.

"We are in a state of shock," a member of the family, who asked not to be identified, told the Canadian Press.

Police said Registre was intoxicated when they stopped him for a traffic violation on Sunday. They say he became aggressive during questioning at the station, forcing officers to use a Taser.

Registre ended up in critical condition at a Montreal hospital, where he died overnight Wednesday.

Registre's death, along with the death of a Polish man after a similar incident on Sunday at the Vancouver International Airport, has prompted Amnesty International to call for a moratorium on Taser use.

"We think the weapon is used too often against people who are not armed and don't pose a threat," said Beatrice Veaugrante, head of the human rights organization's Quebec branch.

Veaugrante and other critics say there has yet to be an independent study in Canada about the safety of Tasers, which are manufactured by the Scottsdale, Ariz., company of the same name.

"It's really worrying to see that maybe police are using them a little too readily," she said Thursday.

Tasers can save lives, research centre says

But figures compiled by the Canadian Police Research Centre suggest that most mid-size police forces only use stun guns between 50 to 60 times a year, on average. They were only used 51 times in 2006 by police officers in Quebec.

The centre's executive director, Steve Palmer, said there have been several international studies that demonstrate their harmlessness.

"There is a growing body of knowledge out there that these devices are safe when used properly," Palmer said.

"We don't speak often enough about the number of lives that have been saved, the number of people that are up and walking around today that might not have been had it not been for a Taser."

'It's Russian roulette,' says brother after Taser death

Yet a number of recent deaths have undermined public confidence in a device that delivers a 50,000-volt shock to suspects.

According to some counts, as many as 17 people have died in Canada following Taser incidents since 2003.

"It's Russian roulette," said Patti Gillman, whose brother, Robert Bagnell, died after being stunned by police in Vancouver.

"They [police] have no idea when they use it on someone what the outcome is going to be," said Gillman, who also runs the blog "Truth … Not Tasers."

A Quebec legislative group is currently studying the provincial government's policy toward Tasers. A government spokesperson told the Canadian Press that following Sunday's incident in Montreal, provincial Public Security Minister Jacques Dupuis ordered the group to hand over its findings as soon as possible.

Palmer said the police research centre has also been considering conducting a more wide-ranging study of Taser practices in Canada.

In the meantime, the Registre family will have to wait for answers about how a routine police operation ended in Quilem's death.

Quebec's provincial police force, which has been investigating the Registre incident since Tuesday, is refusing to comment on the case.

Gillman warned the family to prepare for a trying experience in their quest for information.

"They can expect a long and frustrating journey if it's anything like what we've been through," she said.