Who is Gormogon?

I don't normally blog about Bones because 1) it's a procedural so the same thing happens every week and 2) I'm mainly watching for the unresolved sexual tension, so I pretty much figured that each week my entry would look about like this:

"There was a murder. Booth and Bones solved it with some help from the Squints. There was some witty banter and a few amusing moments in the lab. Booth and Bones didn't do it."

But tonight's episode, the season finale, may be revealing the identity of Gormogon, the serial killer introduced in the season premiere. So I wanted to have my guess written down before I watched the episode.

EW's PopWatch thinks it's Zack Addy's "rival", Dr. Clark Edison (at least I thought they did. Now I can't find it.). That seems pretty reasonable. But I'm kind of afraid that it might actually be Zack. For one thing, I read a cast list for next season (though now I can't find that either. Is this some kind of conspiracy?) that did not include Eric Millegan. And for another thing, over the past couple of episodes we've found out a lot of odd and surprising things about Zack. Last week was the thing about the singing. The week before that we learned that he's "deceptively fit". They underestimate the guy and apparently he's full of surprises. I still can't figure out what his motive would be, but I'm going to go with it being him. If I'm right, this'll be sad. No more "King of the Lab".