You're new, so you might not have heard, but the machine those idiots use to go digging in people's private lives? We have one, too. And since our cultist friend was kind enough to put himself in a position where we can get his dimensional signature--assuming he doesn't bust out of SP custody before then--we can follow him anywhere in space or time.

[Also assuming the other Legionnaires don't come down with an inconvenient case of due process-itis and get in the way of Cortana being nosy.]