I can see why they want to protect his privacy, but I don't see why they cannot release a report with the name of the security guard as well as a video with his face pixelated so that the public can be informed as to what went down. The two dead guys did look like douchebags though and one was known to start fights.
They don't want to release his name exactly to protect his privacy. Doing otherwise opens this guy up for persecution by a politically motivated public mob, including some politically motivated media. He was cleared of any wrongdoing under the law, so not accused, and that's the end of it.
The public knows what went on, without having to see the gory details, pixellated or not.
To go further, I don't agree that any person accused of a crime should have their names publicized, since they are innocent until proven guilty (he wasn't even accused). The court of public opinion, through the trashy media, is quick to render judgement before a trial has taken place. When the person is acquitted, there is never any retraction (well, maybe on page 25 at the bottom in small print) or acknowledgement of innocence, and the person is stigmatized for life.