This has nothing to do with presumption of innocence. Presumption of innocence means that you are considered innocent until legally proven guilty in court. It is a very fundamental value of a democratic justice system that guarantees that you can defend yourself of accusations and you are free of the arbitrariness of prosecutors and public opinion. If you undermine that out of an emotional reaction to some event you risk creating much more harm, by sending many innocents in jail and generally instilling distrust in the society, than you will prevent.

Also, what do you propose? If it is not necessary to be declared legally guilty anymore, then what? The color of your skin? The mood of the prosecutor and judge? The number of times you are presented before the court? What if the cops don't like you? What if you are accused without proof and without mean to exonerate yourself?

The cases you describe of people committing 47 offenses (with no conviction you say, so the justice system decided that they were not actually offenses, Yet you are here claiming that they are without any knowledge of the facts) and then going to kill someone are very very rare. You can't have a 100% failure-proof system without complete totalitarian control over everyone in the population. Many of these people are just insane, they're not the organized terrorist group types, and the justice system is not equipped to deal with mental health issues. When it tries you end up with people in psychiatric internment for years and years without trial and with little recourse, which is another tragedy.