They are trying that of course but it isn't working.
What is surprising to me is how little actual investigative journalism has went into attempting to identify the identity of the leaker. The Russians apparently have some insight into the source IP address of the the person who posted the files to a Russian server. Where is the curiosity in the media about that? Methinks maybe they really don't want to know. Maybe they know in their heart it was grad student at CRU and identifying him/her would open up a can of worms that even the mighty MSM could not stuff back in the bottle.
From what I can see about the collation of the emails, the CRU data was pretty carefully leaked. It would appear to have been collated and edited by someone focused on the issue at hand with careful avoidance of shopping lists, kids with runny noses and sexual partner problems that must permeate the email repositories of any large organization of people, all of whom have personal lives.