Isn't citizenship, or at the very least residency a requirement for treason?
Are you now arguing in favor of Confederate jurisdiction? Had John Brown committed his offense post-bellum, no doubt he would have justifiably been convicted of treason under US federal jurisdiction. When John Brown reached Harper's Ferry, his first act was to take possession of United States' property and overpower United States guards found there. When finally captured, it was by United States troops on United States' property after a fight in which one of the United States Marines was killed.
Are you now arguing in favor of Confederate jurisdiction?