While I agree that "factual" sources abound within Google (and other intenet sources) one cannot ignore the footnoted discussion in sites such as this:
http://www.gunfacts.info/gun-control-myths/guns-in-other-countries/
I've often stated that reliance on "third parties" (police, etc.) for the safety of my family is abhorent I also have stated that, while there appears to be a relationship between gun ownership and the mass killings that occur with frightening repitition, an in-depth study of such events reveal often that the events would not have been averted solely on banning of gun ownership. In most cases the guns used were illegally obtained, meaning we don't especailly need
more gun laws but, rather, enforcement of existing laws.
Personally, I strongly believe there is a close relationship of such violent events and the U.S. government's change in the way it finance treatment those afflicted with mental problems and illnesses.
Back in the '70's or so, the hospitals were suddenly nearly emptied by the reliance on out-patient drug treament rather than incarceration that had been in place for decades. Could be wrong, of course, but the two events seem to have a discernible parralell...