An interesting article from Smithsonian article, December 2001:
Who Was Deep Throat? by William Gaines
"After 36 years as a full-time reporter at the Chicago Tribune, I retired in 1999 to teach journalism at the University of Illinois at Urbana-Champaign. During that first semester, as the students searched for an investigative project to tackle, I showed them All the President’s Men."
<snip>
Why, my students asked, was Deep Throat’s identity still not known after so many years? It was not an easy question to answer. Walt Harrington, a fellow journalism professor at the University of Illinois, once told me he had heard Bradlee say that anyone wanting to learn Deep Throat’s identity should search a computer database for Watergate figures who were actually in Washington at the time of those meetings. To my knowledge, no one had ever done so. Though few organizations would have the resources or motivation to unmask Deep Throat, it seemed a challenging pursuit for my students.
<snip>
"We obtained the 1972 and ’73 White House staff directories, which listed 72 people in high-level jobs; of those, 39 were living males. The students then ruled out anyone not working at the White House between September 1972 and May 1973, the period when Deep Throat met with Woodward. Newspaper reports showed that some promising Deep Throat candidates, including Chief of Staff Alexander Haig, were out of the country during the time of those meetings. Because the reporters had written that Deep Throat drank Scotch whisky and smoked, the students also eliminated confirmed teetotalers and nonsmokers.
That left just seven candidates: Patrick Buchanan, speechwriter and special assistant to Nixon and later a newspaper columnist and presidential candidate; Stephen Bull, a personal aide to Nixon; David Gergen and Raymond Price, both speechwriters; Jonathan Rose, attorney for regulatory affairs; Gerald Warren, deputy press secretary; and Fred Fielding, an attorney and assistant to White House chief legal counsel John Dean."
The students conclusion? Fred Fielding. Now, does anyone know how Fred is doing?
http://www.smithsonianmag.si.edu/smithsonian/issues03/dec03/presence.html