The Bureau officials were working with the Tribe, advocating "their" interests which meant the documents were not exempt from public disclosure of intra-agency communications.
The Bureau officials were working with the Tribe interests. The documents were not exempt from public disclosure of intra-agency communications. This was what these Tribe interests meant. The Bureau officials were advocating "their" interests. The documents were not exempt from public disclosure of intra-agency communications. This was what these interests meant.