Jin was actually in the same tier of power as he was before, a 5th circle, but he had TONS more mana in his body because of his friend's mana method that he was using. To someone else, it would seem as if Jin were a lot stronger than his realm of power, which he actually was.
The beauty of this mana method was that he could use the same amount of effort and mana for more powerful spells because of how much was being contained in his body.
This allowed him to peek inside Karen's memories without killing her, but in all honesty, he didn't care if he broke her mind or not. She was a member of his enemies, and Jin always killed his enemies.
Looking into Karen's mind, he noticed that she wasn't a high-ranking member at all, but since she was the lead detective in the precinct, she was given information that she normally wouldn't have had access to.
These included the grand plan of the Sons of Adam, as well as who their leader was.
