Sure, that increased attention probably makes a difference, but 'gun culture' is not the reason US police forces often seem to do a mediocre job investigating gang vs gang killing. Nor is having guns what makes the killings happen. It's exactly the other way around. They have the guns in order to kill their gang opposition. If you could magically un-invent guns they would be using other tool to do it because the numerous other societal problems which created the environment of desperation hadn't been solved.