As it has been looking lately, this is most likely just another nutcase foreigner that feels like the big boss in Thailand. However, the news information does not say much. Do they have any proof he actually is the right person? If so, they would have arrested him, I guess. That remains to be seen.
If he is the perp and the police see it as he is at fault, then of course the family should have justice. What I am thinking about, is what kind of justice they are looking for? Is that to see the German get a sentence and sent to prison? Or is it just that they are looking for economic compensation, like a great payday? If the latter, my recommendation is that they seek to settle it in a civil case.