This is the opposite of Jim's MOA post. The "failure to warn" part will be interesting - not sure how enthusiastic a struggling retail industry trying to get customers back is going to be about warning customers to danger. (I doubt our local mall is going to post a sign saying, "Warning - gang area - duck during shoot outs." )
The security company's contract was probably limited in what they could do - and, like every other big city, there isn't much impact security can make when cops don't show up, or don't arrest. And what is the city's liability in all of this?