If they don't, leading the public/press to Hatfill looks like a smoke screen to cover the fact they couldn't find whoever - maybe they thought it'd buy them some time, they could catch the culprit(s) and then come out and say "oh, sorry, here's the real culprit(s)".
Ashcroft's reply to this lawsuit should be interesting reading. This suit may finally force him to go public with whatever information he had that put him on HF's trail in the first place. Information that we are not privy to or that has not leaked out, that is.