Good point. I was thinking specifically of gun violence (comparing nations in which firearms are socially acceptable and easily accessible to the masses vs. those where firearms are more of a taboo)
but you're quite right of course in that if somebody wants to kill a bunch of people badly enough, they will find some suitable instrument with which to do it.
Of course, there's a world of difference between the one loony out of a million who walks into a building and starts killing everything that moves vs. the somewhat more pedestrian individual who shoots one or two specific people (usually not with an assault rifle) as retribution for some specific offense.
I'm honestly a bit surprised that nobody has jumped in with the example of Canada. In most regards (at least, amongst those individuals who I know personally) Canadians and Canadian society seem to be very closely attuned, morally and politically, to the US.
I can't seem to recall any mass killing sprees of late taking place in America's Hat, however one paper which I located on the subject noted that "In 2002 there were 149 gun murders in Canada, in the United States, there were 10,800." (source)
Of course, the population of the US is approximately nine times that of Canada (307,000,000 vs. 33,700,000) so if we were to multiply up the population of Canada to match that of the US, the number of gun-related homicides would rise to 1,357, which is still only 12.5%. Is this attributable only to Canada's rather stricter laws concerning gun ownership, or is it due to some other combination of social and environmental factors? Does Canada not have the same wanna-be gangsters as we do in some cities in the US who go around popping one another freely as retribution for drug-related affronts, sleeping with one another's shorties, dissing each other, etc?