Still, Lombard said the public needs to discuss what an appropriate use of force by police is and if those standards should change.

Tasers and other stun guns can fail for a number of reasons, according to RCMP Sgt. Wayne Knapman, the non-commissioned officer in charge of the training section for the RCMP in Nova Scotia and the senior use-of-force expert in the division.

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They tried to use a Taser on Levi multiple times. But it didn't immobilize him, and he was shot and killed by an officer. It's not clear why the Taser didn't work. A coroner's inquest has been ordered into Levi's death.

But the success rate isn't high enough for Temitope Oriola, a criminology professor who studied stun guns at the University of Alberta in Edmonton. He said he doesn't know of anyone tracking how often stun gun failures lead to police using deadly force.

In investigating the suicide in Cape Breton, for instance, SIRT concluded that one of the Taser's darts entered the man's back, while the other landed in the hem of his shorts and did not penetrate his skin.

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"The family continues to be in deep mourning. You know, there's essentially zero feedback on what's happening, no sharing of evidence. [They] let the family sit there and percolate in their absolute grief wondering what the hell happened and how the heck it could have happened."

"Some fields cannot afford any real margin of error," said Oriola. "Within a field such as policing you've got to get it right practically all of the time, and this is where those tensions arise. This tool still needs further refinement."

Rodney Levi was one person a stun gun didn't work on. His family thinks that may have played a part in his death at the hands of police.

There is also a "defensive mechanism" that can counteract the effects of a stun gun, said Knapman, but he wouldn't reveal what that was.

Nova Scotia RCMP say stun guns are effective 87 per cent of the time at making a person comply with police orders, including instances when the weapon is simply drawn and not fired. Last year, its officers in the province drew their stun guns 59 times, firing them in 17 cases.

Lombard wants police forces across the country to cut down on how often they use all their weapons. She said communication is key.

"Had that weapon been more effective than it was, then I believe that we would, obviously, have a different outcome," said Alisa Lombard, a lawyer representing Levi's family.

Tasers are used any time an officer feels they or the public are going to be seriously hurt by someone, said Knapman. If an officer is in that kind of danger, they could also draw their gun. In fact, if an officer is alone in that kind of situation, they would draw their gun and not their Taser.

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In New Brunswick and in Nova Scotia, at least two people have died in recent years after the weapons didn't immobilize them.

In the hands of police, stun guns like Tasers are designed to save lives, but when the weapons don't incapacitate someone there can be fatal consequences — from officers using lethal force to a person continuing to harm themselves.

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In September 2017, a Cape Breton, N.S., man also died after a stun gun didn't work. The man was trying to harm himself by jumping from an overpass, and a Cape Breton Regional Police officer fired his Taser to try to immobilize him. It struck the man but but didn't stop him, and an instant later, he died by suicide, according to a report by Nova Scotia's police watchdog, the Serious Incident Response Team (SIRT).

In some cases, it's not obvious why a stun gun doesn't incapacitate a person. In other cases, it's more clear: For instance, a stun gun doesn't work unless two or more of the darts it fires connect with a person.

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Despite the limitations, Knapman said, Tasers and other stun guns are an excellent tool and make police work much safer for officers and the public. He said in some cases a Taser can safely resolve what might otherwise be a lethal encounter.

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"There's a really big difference between being administered an electromagnetic shock and being dealt a fatal blow from a firearm," said Lombard.

When one of the darts, also called probes, doesn't strike the person, the electric circuit can't be formed and the person isn't immobilized, said Knapman. Loose-fitting clothing can keep the probes from reaching a person, preventing the weapon from working.

David Burke is a reporter in Halifax who covers everything from politics to science. His reports have been featured on The National, World Report and As it Happens, as well as the Information Morning shows in Halifax and Cape Breton.

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Stun guns work by firing a pair of darts attached to wires. When the darts connect with a person's body they form an electric circuit. The wires carry a jolt of electricity that causes an uncontrollable muscle contraction that usually immobilizes someone, forcing them to the ground.

Axon, the company that manufactures Tasers, said its weapons require two or more probes to connect with a target and they must hit sufficient muscle mass to effectively incapacitate someone.

"I mean, how do you jump from one being sufficient to the other being justifiable in a matter of seconds? It doesn't make a lot of sense to me."

In September 2018, there was another incident in Lower Sackville where the RCMP responded to a report of a woman becoming violent after taking drugs. Officers fired a stun gun at her, and the darts struck her midsection and leg. She was momentarily stunned, then removed one of the darts, ending the effects of the weapon.

In an email, the company said police forces need to clearly identify why a Taser doesn't work and if it was caused by environmental or situational factors versus a weapon error. Figuring out the cause of the failure will determine whether more officer training is needed or if a weapon needs to be serviced.

He said there are no long-lasting effects from the use of a Taser compared to weapons like pepper spray or a baton. He said a Taser jolt lasts for five seconds, versus pepper spray, which can be painful for an hour or more.

Oriola said when stun guns don't work, the person who was hit with one can become even more agitated and lash out. He said police forces across the country use stun guns far too frequently and should focus on de-escalation, ways of calming people down to reduce the chances of conflict.

In October 2017, a man in Lower Sackville was trying to harm himself so officers used a stun gun on him, but it "appeared to have minimal effect as the AP (Affected Party) continued to be combative," said a SIRT report.

On June 12, officers responded to a complaint of an unwanted person at a home near Miramichi, N.B., according to an RCMP spokesperson. When they arrived, RCMP said, they faced Levi, who was holding knives.

Axon said when a person is not incapacitated by a Taser it is usually because one of the required conditions for the weapon's functionality are not met.

"It is an electrical device, there are times it can fail for multiple reasons … we can't rely on that one tool, we have to have multiple options," said Knapman. "All our tools have the possibility of failing, even our firearms."