Expecting all newcomers to operate under the same set of laws is unrealistic to begin with, but that is another issue. However what more evidence could have been needed beyond the identification of the one responsible by the victims? Why was someone known to be killing people allowed to continue doing so?

And your witnesses, I presume, were hunters, and if they were at the grounds when it was attacked then surely they were participating in this hunt. Now they can no longer, rather than whatever deal they might have been given for their cooperation.