My response is there were many people (primarily engineering students and professors) who might have seen the shooter during the previous weeks - but it is only the former student who given his background of being homeless and being extra vigilante as a homeless person noticed the shooter as suspicious and even followed him to his car that led to the tip.

Many in tech will quote Steve Jobs "you can't connect the dots forward, only backwards" speech, but this guy whom I don't know, I like to believe he lived it. Flip your question on your head, would you be willing be homeless for 10 years and in the process help catch a school shooter?