Mr. Z
Quotes are from Hatfill v New York Times case text.
SHEDD, Circuit Judge (summarising): Nicholas Kristof writes a regular column for the editorial page of The (NY) Times. During the spring and summer of 2002, Kristof wrote several columns criticizing the FBI's investigation. From May through July 2002, Kristof focused his attention on the FBI's handling of information related to a man he called "Mr. Z." According to Kristof, circumstantial evidence pointed to Mr. Z, who was widely suspected by other scientists of involvement in the anthrax mailings.
In Kristof's opinion, the FBI had not moved aggressively enough against Mr. Z. In August 2002, Kristof identified Mr. Z as Dr. Steven J. Hatfill, a research scientist employed by the Department of Defense.