The NYPD wanted to go public with it, and was threatened by the DOJ. What do you mean "publish"? I said go public with the discovery of the emails. The FBI would have looked foolish if that were to happen.
But, to your original point, this explains why Comey made the announcement ... he had no choice.
http://www.breitbart.com/radio/2016/11/04/erik-prince-nypd-ready-make-arrests-weiner-case/