If you or your injured employee isn't satisfied with the police response, take your case to the local news media if you think it is serious enough. I'm not sure what the HIPAA minefields are in this area. Even when privacy issues exist, there are ways around them. Don't make "bad publicity" for the hospital your primary concern. The public will demand action. .
I had a conversation recently with a friend who is an emergency room employee about hospital violence. He rolled up his sleeve to show me a years-old bite scar on his forearm—a memento from a drug-addled patient who'd slipped his restraints and taken a chunk out of my friend. As if the fear and violence of the assault itself were not traumatic enough, he had to undergo blood tests to ensure that he had not contracted hepatitis.
That should not be part of the job description.