Several points stand out to me as significant.
Fetzer seems like a Truther and not a professor
By this I mean more than just his factual information and the rhetoric of his statements. The interesting thing to me is that Fetzer would continue with a correspondence that he clearly finds beneath him. He's not just frustrated with someone who doesn't understand what he's saying. He seems to see this whole discussion as beneath him, yet continues writing to Brass. It reminds me very much of the kind of Truthers we see here on JREF and that I have met elsewhere. They will never stop repeating their Truther mantras over and over and over again, even to those who have lost interest in hearing. He threatens to stop the correspondence, but doesn't.
Honestly, I had not expected Fetzer to be so obviously like a Truther.
He shows phony Truther suspicion
The first part where he asks about academic e-mail leaves me wondering if he thinks Brass may be a spy of some sort. He uses words like 'shill' to describe Mark Roberts. Apparently he believes there are Kennedy assassination investigators who have 'disappeared'. I guess he believes the NWO super secret government sends around spies dressed up as students to find out what super important info has has on them.
This leaves me thinking that, like a lot of other educated Truthers you see here and elsewhere, he is frustrated that no one will listen to him. Fetzer is a professor and used to being listened to just because of that. He seems to find it very frustrating that people laugh at him and treat him like a joke. I suspect he feels he should be listened to no matter what he says. Or rather, that what he says is the measure of what should be listened to. What you see here is the result of years and years of being ostracized professionally and being treated like a joke by large numbers of students.
Anyway, those are my initial thoughts on this.