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"(1) Col. Boylan is denying authorship of the original email to me but is acknowledging having sent the subsequent emails, even though the tracing information on all of those emails -- including the "fake" one -- strongly suggest they came from the same computer;"
It's fairly trivial to fake this stuff, especially if you know what version of Exchange (or other mailserver, but Exchange in this case) the military in Iraq is running. Getting that information would be trivial. Just send a message to Boylan himself and you get the mail headers that you need to spoof.
Even if it's not the case that someone hacked the military mail server, or spoofed it, there's every possibility that Boylan could have left his computer unlocked (bad security practice, but common enough) and walked away. At that point, anyone with a grudge against Glen or Boylan who had access to the room could have sent the message. I'm not saying the Boylan didn't send the message. I am saying that you can't prove it by this.