I'm not sure one can put it down entirely to US "gun culture". Even though guns are pretty easy to get hold of, many more Americans are killed with knives than most other countries. I recall one statistic that far more Americans are murdered by chairs alone, than every type of murder put together in the UK.
And although Ivor may be correct that in Michigan you need to be a US citizen to buy a handgun, one must of course add the word "legally", since there are far more guns than people in the USA.
Gun ownership by itself isn't a great predictor of whether a country has a lot of murders.
At one extreme is Switzerland where every adult male citizen is required by law to keep military grade hardware in his home. Yet their use in crime is quite rare. It's neighbour Germany has pretty tight gun control yet more gun crime.
Ironically, the American idea of a "citizen militia" does seem to reduce gun crime. Where gun possession is actually part of a structured defence process, they are less often used from crime. Armed Israelis don't kill each other much. The USA has had conscription, but that's not the same thing at all. Almost all gun crime is by people who have had no formal training with them.
What no politician in America on either side of the debate is prepared to say, is that Americans like killing other Americans, but once you've grasped that, then gun control itself is not the core issue.
The death penalty can thus be seen not as a deterrent (because it isn't), or a form of justice (unless you're executing a black man), but as part of this apparent "wish" to kill each other.