http://en.wikipedia.org/wiki/2002_Karachi_bus_bombing http://en.wikipedia.org/wiki/2002_Karachi_bus_bombing could qualify (a bit short of the 20 casualties, but

http://en.wikipedia.org/wiki/2002_Karachi_bus_bombing http://en.wikipedia.org/wiki/2002_Karachi_bus_bombing could qualify (a bit short of the 20 casualties, but not for lack of trying).