Although what you suggest is appealing…One must remember that laws are written from the perspective of the overall working of the state machinery. One act committed in defiance of the law or the spirit of the constitution can have huge repercussions. While people’s part could have aided in said case, no government wants to deal with vigilantes. Also, people are responsible for the protection of life. That includes one’s own life as well. If the citizens are not safe, it can only be assumed that the administrative authorities are not working to their full extent. just as is suggested, any democracy that wishes to keep its citizens out of harms way would use the same approach to tackle this problem.