Two reasons they didn't go after the guy who "confessed". First is the fact that no crime was committed and second is the fact that Armitage didn't lead them to the white house.
Bingo. The drumbeat at DU is now starting for further investigation into the forgeries that started this whole thing and their speculation about Cheney's possible connection to them. I say bring it on. Wilson and Vincent Cannistraro both are on the record saying they had seen the documents before they possibly could have. If we can get to the bottom of this, we can prove what we have suspected all along...that this was an attempted coup by rogue agents and ex-agents at the CIA.
There ya go. Motive.