The Smithsonian article does not name the suspect [James Brubaker, if the earlier reports hold] but notes that an indictment is (still) expected. More if I can get it.
[Update: Thanks to MTHistory for adding a comment. Yes, the Great Falls Tribune is reporting this afternoon that James Brubaker,
[Further update: Television reports say Brubaker was charged with interstate transportation of stolen property, and add "Authorities say hundreds of maps and lithographs found during the search were in envelopes ready for sale on the Internet."]