Hamilton had a history of interest in guns, was the legal owner of the firearms used in the shooting and a popular member of local gun clubs. http://en.wikipedia.org/wiki/Thomas_Hamilton_%28spree_killer%29
In hindsight both of these men were suspect & should never have been granted gun licences.
Thanks for posting this link Doug, it has reminded me and confirmed my memory of a number of facts around this case. Specifically the clubs that Hamilton claimed to be a member of were not equipped to operate the calibre of pistol he had on his licence. Also Hamilton was not able to demonstrate regular or appropriate use of those pistols. The Police and clubs involved with him should never have been party with allowing him to obtain or retain these firearms.
Of course Hamilton would have done something else, and probably just as murderous, if he did not have access to firearms purchased 'legally', but his ability to do so would have been restricted if the existing adequate laws had been applied. Hamilton was a gun nut, a paedophile, and a sociopath, he wasn't a pistol shooter.