First time criminals with no police record can legally get themselves a gun and then go out to rob a shop and murder the clerk while they're at it. That's a sad fact about our country.
Do you know how often a crime like that is done with a legally bought gun though? A criminal would have to be incredibly dumb to buy a gun legitimately and then commit a crime with it. From what I understand you can match bullets to the rifling of a gun barrell, and if not, Police could run checks on all guns of that caliber bought in the last week/month whatever and then investigate based on that.
Lets say even IF that wasn't possible and the man had no access to a legally bought gun, he could buy one on the black market, and I would imagine that's where most guns used in crimes are acquired. Making guns illegal wouldn't change their availability.
I think the biggest problem with legally bought guns would be domestic violence and the like, or crimes of passion/mistaken identity etc, which is why I think Austarlia's laws regarding storage, inspections and background checks to be adequate. And once again, if it's a 'spur of the moment' crime that is caused by rage or something, then I imagine a stabbing or something would be just as likely if they didn't have access to guns.
Now finally, I do think there should be restrictions on the types of guns people can own. I don't think Semi-automatic and full-automatic weapons have any place in homes. They are totally unnessary for hunting and sports/recreation, and unless you're fucking Tony Montana, I doubt you'll need a gun like that for home defense (I don't think having guns for home defense is a good idea in the first place though, another reason I support Australian laws demanding a justification of sport/recreational shooting).
Also I'm going to split these posts into another topic, thanks to everyone for keeping insults to a minimum, I know this sort of discussion can get heated.