You're asking the wrong questions. It's not which laws didn't work, it's about finding some that do. Bad laws get bad results, we all know that. But that's not to say that there aren't any good laws that work. Or that we shouldn't keep trying to find the right laws that work. You could start asking: why do other countries not have these kinds of massacres, and what are their laws regarding firearms? This would be a good place to start.
You really don't have a clue in the world, do you?
The Top 5 Worst Gun Massacres by an Individual
Perpetrator Location Date Victims
1 Anders Behring Breivik Utøya Island, Norway 22 Jul 2011 77 killed, (151 wounded)
2 Woo Bum-Kon Sang-Namdo, South Korea 26 Apr 1982 57 killed, (35 wounded)
3 Martin Bryant Port Arthur, Australia 28 Apr 1996 35 killed, (21 wounded)
4 Seung-Hui Cho Blacksburg, Virginia USA 16 Apr 2007 32 killed, (25 wounded)
5 Campo ElÃ*as Delgado Bogota, Colombia 4 Dec 1986 30 killed, (15 wounded)