He claims he did it so he could work at home. Is it possible he was intentionally exposing classified information? It could have been picked up by a back door at AOL, a tap on his home phone line, or off of his hard drive.
I used to do something like that to store FR threads I was reading at work: I'd open FR in one Window and in another Window I'd log into my email account using my server's remote access feature; copy the info I wanted into an email addressed to myself; then email myself so that when I got home and downloaded my emails from my server I'd have a storage copy on my PC. Of course I wasn't the Director of the CIA, so I wasn't concerned about security issues. But if someone had wanted to intercept my email when I was doing that, all they'd need to do would be to remotely log into my email account before I downloaded it from my server to my PC.