Author: Alfred Montestruc
The paper is entitled 'Firearms and the Decline of Violence in Europe: 1200 -2010'
Here is a graphic from the paper.
As you can see homicide rates were rising in Europe and the British Isles from 1200 to 1500 AD, suddenly they dropped just after 1500 AD. Then leveled out, then dramatically dropped again circa 1621 AD, and ramped down till around 1800 AD.
In around 1500 AD the wheellock firearm was invented. It was expensive, but it was the first ready to use portable firearm. One could keep a small wheellock pistol in your pocket, draw and fire at a would be robber.
In 1621 the flintlock was invented. The flintlock was cheap, and could be afforded by relatively poor people, thus everyone could have a small portable ready to use firearm.
For some strange reason robbing people went out of fashion, ,
The data speaks for itself, but we know that armed robbery was common in Europe prior to the invention of ready to use firearms, moreover it was a relatively safe sort of crime for the perpetrators.
The conjecture is that robbery of sometimes gun armed merchants or travelers became suddenly much more likely to be fatal to the robber, and that in many cases, gangs of robbers confronted with a firearm, chose discretion over valor. They could "win" the fight, at the high probability of a death or serious injury of one of the robbers. That made robbery an impractical crime.