Jack is not sympathetic. He's clearly using Charlie.
Even if he actually is in love with her, it's obvous that he's okay with putting her in danger in order to make an arrest. He's also pretty cavalier abouth the mental anguish he's causing her by telling her for a certainty that her uncle is a murderer (as he is, but it seems apparent that neither Jack or Saunders are at all certain about that at this point).
Although he's probably the most sympathetically portrayed law-enforcement figure in a Hitchcock film, he still does not come off particularly well in my opinion. I suspect that Hitchcock did not much care for the character either.
Thoughts?