Whatever the 'explanation' for these apparently pointless murders turns out to be - whether its origins lay in a family property dispute, a row with fellow cab drivers over status, or taunts about being a 'mummy's boy' (depending on which tabloid you believe) - there's surely something to be said here about male anger, and the easily wounded pride inherent in certain kinds of masculine identity.
As I listened to neighbours and friends describing Bird as a decent, ordinary type, I was reminded not of Dunblane or Hungerford - this wasn't a psychopath or someone already known to the authorities - but of those news stories about men who suddenly and unaccountably flip from being doting fathers to murdering their children. As in the case of Bird (who began his deadly spree by killing his twin brother), their intense male narcissism can't conceive of anyone surviving and thriving without them. If they have to go down, then they're going to take everyone else - including their 'loved ones', whom they actually only love as reflections of themselves - with them.
I'm not sure what the answer is, but despite the currently unfashionable nature of this kind of gender analysis, we need to keep asking the questions...