I don't really see the problem with what the paper have done. The more people see the picture the more likely he is to be identified and dealt with. Can't think why the Mail wouldn't want to print the story.
That said, I'd imagine he was just acting a bit of a tit, and didn't really harbour murderous intentions. Unless he has previous, I hope they catch him and caution him to scare him out of such silliness in future.