The "victim" had been a prior participant in a a violent MetroLink robbery. Pleading guilty to that, he was free to "move about the country".
http://www.stltoday.com/news/local/crime-and-courts/man-killed-in-shooting-on-metrolink-train-had-robbed-man/article_eb441c1a-6771-5a7f-bd57-6bf034846a1e.html
I guess a violent robbery doesn't get much jail time these days.