Mika, probably the Swedish system is the way it is because there was never a need for something stricter, such as has been the case in the U.S. Justice systems usually fit the culture to which they belong, it therefore makes no sense to compare the U.S. justice system to the one in Sweden. There are completely different circumstances, different histories and different views at play here.
Also, has it occured to you that perhaps the man lashing out today was mentally ill? If he wished to kill someone, why do it in full view of the public? I'm not making excuses for him, simply giving you something to think about.