Since Australia moved from from relatively lax gun laws to strict gun laws there has been a reduction in mass shootings. The same happened in the UK. Less guns in circulation results in less mass killings. Simple.
There is more on the BBC website, http://news.bbc.co.uk/1/hi/technology/4780963.stm with some nice old adverts for the PC. http://news.bbc.co.uk/1/shared/spl/hi/pop_ups/06/