Aye, there be witchery afoot...and witches are a wiley lot. I think that is why torturing them after they're finally captured is so gratifying. There have been instances when I, after having recieved a full confession in record time, have started backtracking, just to prolong the inquisition. "Are you sure you're a witch? Are you really, really sure?". It usually comes full circle, and they start swearing up and down that they are not a witch again, and I must start all over....which suits me fine. Doing God's work is never boring!
I don't know how to eradicate your problem with the old hags, other than to suggest that you sit back, relax and let Jesus do the wetwork....He'll get them in due time! Our Lord is nothing if not tenacious!