In Slavery in Massachusetts, Thoreau writes:
Again it happens that the Boston Court-House is full of armed men, holding prisoner and trying a MAN, to find out if he is not really a SLAVE. Does any one think that justice or God awaits Mr. Loring’s decision? For him to sit there deciding still, when this question is already decided from eternity to eternity, and the unlettered slave himself, and the multitude around have long since heard and assented to the decision, is simply to make himself ridiculous. We may be tempted to ask from whom he received his commission, and who he is that received it; what novel statutes he obeys, and what precedents are to him of authority. Such an arbiter’s very existence is an impertinence. We do not ask him to make up his mind, but to make up his pack.
Having looked up pack in Wiktionary, methinks the author may allude here to assembling (making up) the people responsible for the enforcement of his judicial decision (a pack of dogs / wolves that hunts an innocent victim, i.e. Anthony Burns). Does Thoreau mean here something else?