WHEN an electronic gun designed to immobilise but not kill emerged from the pages of science fiction and went into manufacture a decade ago, police forces around the world snapped it up. Instead of shooting suspected criminals who posed a threat, they could now zap them with 50,000 volts of electricity and have them safely in handcuffs before they recovered enough to resist or flee.

But are stun guns really non-lethal? Canadians have been wondering since a Polish immigrant died last October at Vancouver airport after police subdued him with a Taser, the most popular brand of the electronic weapon. An amateur video of the incident posted on YouTube sparked a public debate, and several official inquiries. On July 22nd a 17-year old youth in Winnipeg became the 21st person to die in Canada after being fired at with a Taser.

The gun’s American manufacturer, Taser International, has sold 300,000 of them to police forces in 45 countries. It contends that just because someone dies after receiving a jolt, it does not necessarily follow that the Taser was to blame. It says—and some doctors agree—that pre-existing heart conditions, drug and alcohol abuse, and the agitation of having been pursued are all more likely causes of deaths in police custody. Tom Smith, Taser’s chairman, told a committee of Canada’s Parliament earlier this year that although 50,000 volts sounds like a lot, a static charge from a doorknob is almost as high.

Such arguments have proved persuasive with juries. Taser International has won or had dismissed 71 lawsuits for wrongful death or injury. Most of these cases were in the United States, where just over 300 deaths following Taser use have been recorded. (The company suffered a rare courtroom loss earlier this year when a Californian jury ordered it to pay $6.2m to the parents of a man who died after being shocked. It is appealing.) A company spokesman points out that no medical examiner in Canada has pointed to the Taser as a contributing factor in any deaths.

Yet doubts persist. In June the parliamentary committee urged the federal government to commission independent studies. Amnesty International, a human-rights group, wants a temporary ban on Taser use until the research is complete. None of the official reviews backs that, but they call for tighter rules on the use of Tasers and better training for officers who handle them. The Saskatchewan Police Commission has reversed a plan to deploy more Tasers and is restricting their use to specialised teams. By limiting the use of conventional guns by police the stun guns may indeed save lives. But Canadians do not like their police to be trigger-happy, even with “non-lethal” weaponry.