The killing of Daunte Wright, a young black man, in a suburb of Minneapolis in the US, was because an officer mistook her gun for a Taser, according to police.
So how is it possible to mix up the two weapons?
How are Tasers meant to be used?
Tasers fire small dart-like electrodes that can deliver a high-voltage shock to disable temporarily a suspect and allow officers to deal with violent, or potentially violent, people at a distance.
They are used by police forces around the world.
Almost all American police departments now issue their officers with Tasers, according to one assessment.
The US-based Axon company, which developed the Taser used by the Brooklyn Center police department involved in this incident, was quoted as saying their weapons were designed to be distinguishable from handguns.
It had "implemented numerous features and training recommendations to reduce the possibility of these incidents occurring" - including making them look and feel different from a firearm.
Distinctive Taser features include that they
- are often produced in bright colours
- weigh significantly less than police guns
- typically have different grips
- have no trigger safety mechanism, as most guns do
Police officers are typically trained to keep guns in a holster on their dominant side to avoid confusing it with their Taser, which is kept on the belt on the other side of the body.
The Brooklyn Center police manual says that officers must position Tasers "in a reaction-side holster on the side opposite the duty weapon".
"So if you're right-handed you carry your firearm on your right side and [you] carry your Taser on your left," Brooklyn Center Police Chief Tim Gannon told reporters after the shooting of Mr Wright.
He added: "This appears to me... that this was an accidental discharge that resulted in the tragic death of Mr Wright."
What could have gone wrong?
The video of the incident that was circulated by police shows the officer shouting out "Taser, Taser, Taser" before shooting, and then appearing to realise she had used a handgun instead.
The officer has been named as Kim Potter, who had worked for Brooklyn Center Police for 26 years. She has resigned, and been charged with second-degree manslaughter.
We don't know all the circumstances, and the police are investigating what happened.
However, experts say weapon confusion does occur, and that training is the key to preventing such incidents.
"This comes down to how often she trains with the Taser," US-based policing consultant Jeff Noble told the BBC.
"It's a tool that doesn't get used very often. You do have to do ongoing professional training."
The Brooklyn Center police manual says officers need to be trained at least annually, and the training should include "performing reaction-hand draws or cross-draws to reduce the possibility of accidentally drawing and firing a firearm," according to Reuters news agency.
Other experts point out that even if a Taser and a gun are holstered on different sides of the body, if they are both worn in a such a way that they can be easily accessed by the dominant hand, that could lead to mistakes when under pressure.
Has this happened before?
Mistaking a gun for a Taser is rare, but it has happened before.
Comprehensive nationwide figures aren't available.
However, a law journal published in 2012 found nine examples of police officers accidentally using a handgun instead of a Taser between 2001 and 2009. Two of these incidents resulted in death.
There have also been more recent instances of a suspect being shot instead of Tasered:
- In 2015, a man was shot dead in Tulsa, Oklahoma, by a volunteer sheriff's deputy who had accidently pulled out his handgun
- In 2019, a police officer in St Louis, Missouri, mistakenly discharged her revolver and seriously wounded a shoplifter