I would say poverty has more to do with the murder rate than anything else.
If you want to go and rob houses or join a gang, you'll get a gun, legally or illegally. This happens everywhere, not only where guns are legal.
If you can't get a gun, you'll get a big knife or a baseball bat.
The USA is rich in GDP per capita but has patches with poor people with little to lose.
In many EU countries there is far less people with little to lose, even among the poor ones.
Crime in EU is, similarly, disproportionally caused by those who have little to lose, eg. illegal immigrants.
Murder clearance rate by police has more to do with murder rate.
You are much more likely to get away with murder in the US (where clearance rates are 60% at best) than you are in Japan or the UK (where clearance rates are above 90%).
If you want to go and rob houses or join a gang, you'll get a gun, legally or illegally. This happens everywhere, not only where guns are legal. If you can't get a gun, you'll get a big knife or a baseball bat.
The USA is rich in GDP per capita but has patches with poor people with little to lose. In many EU countries there is far less people with little to lose, even among the poor ones. Crime in EU is, similarly, disproportionally caused by those who have little to lose, eg. illegal immigrants.