The blame falls squarely on the shoulders of the one who pulled the trigger and to say that others had a hand in this is pretty ignorant. Personal accountability implies personal responsibility and there isn't enough of this going on. Remember the "Twinkie Defense" when Moscone was shot and killed in SF...while I am in favor of good citizens being able to keep and bear arms doesn't mean that everybody should be carrying loaded guns around town like the Wild West. I will keep guns in my house for personal protection...I will shoot anybody trying to break into my house and I will shoot anybody who would try and hurt a member of my family.
The problem we face as a society is that we live in a 'Fallen World' where there are mental defectos who run around freely. The Law cannot protect it's own citizens until a perpetrator takes action against them first,,,then the Law steps in. Yes, there are writs of protection that only go so far as to keep people away from each other in terms of feet/yards but if a person really wants to harm another a protection order means nothing.
Innocent people were killed and that saddens me because we do not have a system in place to keep crazy people from doing crazy things...a 3 day psychiatric hold in a facility is not the answer as on the 4th day they are out again doing crazy things. There is an answer to this but most people do not want to do it or are unwilling to do it...it goes back to training in a family environment and producing normal and stable human beings...miss this step and we get to deal with ugly things like we see today in the news.