All of these messages were posted from the CDC in Atlanta (these aren't all that were sent from the CDC, just a representative sample). While "cdc.gov" doesn't appear in the headers, doing a traceroute on the IP addresses given as the NNTP-Posting-Hosts, 188.8.131.52 and 184.108.40.206, show that they are machines inside the CDC. Message IDs have library.airnews.net, another Internet America marker.
When I contacted airnews.net, they said "we just give them a newsfeed" which I assumed meant that they give the CDC a newsfeed--it is possible, though, that they were referring to an individual who'd subscribed to their service. In any case, the IA name often appears in the Organization header of each message. Hillyard did make posts using the airnews.net news servers in his own name or using his email addresses at afn.org, inetnow.net and interamp.com. The last entry in the path statement, news.iadfw.net, is a news server at Internet America. Note that in every message the X-Newsreader: line for the message sent from those two machines is the same, even though the messages claim to be from different people. He switched to a third machine (220.127.116.11) and a different newsreader to send forged cancellations of the messages of those who did not agree with him. A fourth CDC IP address, 18.104.22.168, later appeared in messages Hillyard posted to rec.sports.football.college giving two of his real email addresses. That makes it even more obvious that it was Hillyard--not someone else at the CDC--who was posting those messages through airnews.net.
Five of these messages are forged cancellations of five different MindSpring users' posts to atl.general that disagreed with Hillyard in his various personas.
Hillyard has recently claimed that, because he was a contractor, he didn't have access to the CDC newsfeed. He certainly had access to their internet gateway, and posted to various newsgroups using it.
According to Detective Wynne of the Dekalb County Police and FBI agent Bob Kelley, every non-work-related message Hillyard sent using the CDC's computer system (harassing or not) could have been counted as a separate felony count. Misuse of federal property is a crime (I don't know the precise wording or statutes). Unfortunately, because the CDC could not show an immediate financial loss due to the misuse, they declined to prosecute.
7/17/96 - posted to rec.sport.football.college as firstname.lastname@example.org (Nacho Mama), signing as "Jim Legg." He then posted four messages to atl.general as email@example.com (The Centipede), signing as "Mr. Legg." He was using a machine at the CDC with IP address 22.214.171.124. Each message essentially had the same message--that MindSpring's WWW and FTP servers had been down that morning for five hours: message 1, message 2, message 3, message 4. He then switched to a bogus address of firstname.lastname@example.org, signing himself "Aaron." First he claimed to be someone who knew me from Mensa, then he seems to have forgotten who was pretending to be and replied to a post addressed to Duck as Duck.
7/18/97 - Hillyard posted a message to atl.general using inetnow.net's news servers but with his email address and name configured as "library.airnews.net (Richard Hillyard)." The subject line of the message was "This is the Real Richard Hillyard" and in it he swore he wasn't the person who posted the Centipede and Duck messages and that he was innocent of everything else being discussed.
On 7/19/96 between 3:03pm and 3:15pm EST Hillyard forge-cancelled 57 messages posted by other people (Richard Turner, Todd Lewis, Miseries, SubHuman, and Hussein Essawy) from a machine inside the CDC with IP address 126.96.36.199.
7/26/96 - posted a message to alt.test with subject line of "Ignore this!" from a computer at the CDC.
7/30/96 - posted a message to rec.sport.football.college as email@example.com from a machine inside the CDC with IP address 188.8.131.52. He then posted three other messages as firstname.lastname@example.org, using the same machine. In the first he remarks that he doesn't like anonymous posters (how ironic). In the second he says that "military service was the last refuge of the incompetent." In the third he hurls a freebie insult at Trent Woodruff for no reason other than his habitual nastiness towards the man.
8/14/96 - Hillyard reappeared in atl.general, posting as email@example.com in a thread with the subject Re: ISPs in Atlanta to take a swipe at me. He was again using the 184.108.40.206 machine at the CDC. He then posted another nine messages to rec.sport.football.college:
8/20/96 - Another busy day. Posted a message from the CDC using inetnow.net's news servers to atl.general with firstname.lastname@example.org in the reply-to field. He then cancelled the message from within the CDC (220.127.116.11), as well as sending two more cancellation messages for that same message through his interamp.com account.
He also posted as email@example.com, then cancelled the message from the 18.104.22.168 machine. He also cancelled other four messages he'd posted, but I don't have anything showing their content.