User blog comment:IamJakuhoRaikoben/Chapter 369: The Place Prayers Reach, Review./@comment-5598380-20140201001146/@comment-7418318-20140201173405

From everything that happened, I think it's more likely that Tartarus was after Face and even know about the sealers (just their numbers and them being former or current council members, but not their identities) already before Crawford switched sides.

Because if he'd been on their side from the beginning, they wouldn't have needed to blindly strike out against all former council members, but could have gone specifically after the sealers. While they wouldn't have had any qualms about unnecessary killings, it would have saved them time, effort, ressources and would have given their opponents less time and reason to prepare against them.

The most likely time for Crawford's betrayal is the destruction of the magic council I think. He was either afraid they'd find and kill him, or he wanted in on the spoils of war that go to the victor.