I only just heard about it, but I'm almost willing to be that this is gang-related - maybe a Triad payback or something.
Police have commended students for risking their lives to tackle this nutter - otherwise other lives may have been lost (unless the targets were specific).
Incidentally, here's a list of recent mass shootings in Australia. There aren't many - but even one is too much.
August 9, 1987 - Julian Knight opened fire at random on Hoddle Street in inner Melbourne, killing seven people. He was jailed for life.
December 8, 1987 - Frank Vitkovic shot dead eight people and injured four more at the Australia Post building in Queen Street, Melbourne. He then threw himself out of the 11th floor window.
August 30, 1990 - Unemployed Paul Anthony Evers, 35, killed five people with a 12-gauge shotgun in the inner-Sydney Surry Hills, after one of his neighbours called him a "dole bludger".
August 17, 1991 - Wade Frankum fatally shot six people with a semi-automatic rifle and hacked a 15-year-old girl to death with a knife, at the Strathfield Shopping Mall in western Sydney. He then shot himself.
April 28, 1996 - In one of the world's worst mass shootings, Martin Bryant shot dead 35 people at Port Arthur in Tasmania. He was jailed for life.
October 21, 2002 - Two people shot dead and five injured in shooting during a tutorial at the Clayton campus of Melbourne's Monash University. Man arrested.