This is gross negligence on the part of the hunter and he will eventually be prosecuted. Unfortunately that won't bring back the young man so senselessly killed. The number one rule of hunting is to always identify what you are aiming at before taking a shot.
A woman hiker was killed in Washington State a couple of years ago by a hunter. She was hiking in foggy conditions on a popular hiking trail and a 14 year old hunter who had been dropped off with his brother by a grandparent also mistook her for a bear. He did not have a clear view of her, she was on the trail and had stopped to take off her pack and was bent over. He was eventually convicted of manslaughter, but that won't bring the woman back.
I had been on the fence about buying a blaze orange pack cover for fall hiking and this story is the tipping point.