What's the difference between Norway and Sweden?
The two Scandinavian countries are both affluent, with a commitment to liberal democracy and the welfare state. But there's one crucial difference; in Norway, police are not armed as a matter of course. But in Sweden, they regularly carry guns.
The result? According to a 2010 study by Johannes Knutsson and Jon Strype, there are fewer injuries and deaths among Norwegian citizens.
Police lay flowers at the scene where two female officers were killed in Britain
Dr Peter Squires, an expert on gun crime at the University of Brighton, says the study is not unusual.
"Just the fact of arming the police means that they approach incidents more aggressively, there are more armed incidents, more people get shot," he tells The Huffington Post UK.
That's one of the reasons why the UK, like Ireland, Norway and New Zealand, doesn't routinely arm its police - in contrast to the rest of the European world and north America.
According to New Zealand police chief Peter Marshall, there's another reason why they don't routinely armed police: "International experience shows that making firearms more accessible raises certain risks that are very difficult to control."
In 2010, the Washington Post calculated that out of 511 police officers killed by guns in America since 2000, 55 were killed by their own guns, or when the gun of another office was used against them.
But it's not just the increased risk of violence, it's also about how police go about their job.
So why do police have arms at all? Paul Beshenivsky, the widower of murdered police constable Sharon Beshenivsky, has become the latest to call for the routine arming of officers in Britain - saying it will help officers' confidence.
In the US, Colonel Richie Johnson, West Baton Rouge Sheriff's Officer, told the BBC he couldn't imagine the police not being armed, asking: "What does a British police officer do if someone comes out with a knife? Is he supposed to get out his knife and fight him?"
But as Jenny Jones points out in a blog for The Huffington Post UK, the majority of police are opposed to carrying arms.
"A 2006 Police Federation survey showed an overwhelming majority (82%) of police opposed the routine arming of on-duty police officers. Despite a rise in terrorism and gun-related crime since similar surveys in 2003 and 1995, officers questioned remained steadfast in their opposition to armed policing."
Dr Squires points out the a change in Britain could "changes the relationship between the police and the public. It has wider ramifications in terms of how people look upon and interact with the police."