We knew that he was a spy about a day after he joined. We also gave him a lot of information to pass on to the alliance, which he did very nicely. It was easy to figure out really. He asked a lot of questions about things that he wasn't involved in and our spies in the other tribes saw the exact same information showing up within about a day of him joining T:V. Since we had when he joined about 300 villages or so that we needed to noble, we just let him sit there and then when we had finished our current ops we targetted him and he decided to "quit".
The other person that was supposedly "spying" on T:V decided on day 1 after we found out that Doinky was a spy that he liked T:V a lot better than the alliance and has become a highly active member of T:V. He has worked extremely well with our players and has been capping enemy villages like crazy.
If I had to guess, he joined T:V to spy on us, but when he realized that this game is a lot of fun when you play with good players and coordinate with them he decided that it would be better to play with us. We've had a lot of spies on our forums before. There have been a lot of posts in the past about getting spies into T:V. The funniest part is that they haven't done a damn thing. They haven't actually helped the alliance stop T:V anywhere. Doinky is pissed because he was so terrible at spying that he got caught in less than a day. Heck, we were already claiming his villages for later on about day 3 of his being in T:V.