I don't know anything about the law I admit it. But couldn't they have got him for 'involuntary manslaughter'? You need an unlawful act (well he basically assaulted someone without provocation), you need the act to be obvious that it would harm the person (shoving someone with their hands in their pockets to the floor is never going to end painslessly), and you need it to be a substantial cause of the death (it would be a bit of a coincidence if it wasn't). So where's the problem? You'd think it was a done deal.
Have you ever sat on a jury. It's a fucking nightmare.