According to his Wikipedia page...
http://en.wikipedia.org/wiki/Leland_Yee
The guys he was buying weapons from were Muslim terrorists located in the Philippines. It's also odd that he was associated with the Chee Kung Tong, which I remembered vaguely hearing about before. It's an interesting name, associated with a Masonically based secret society. The name also recurs on all kinds of businesses throughout the US. In addition to criminal behavior I vaguely remember it's been linked to both The Occult and Chinese Intelligence.
While a lot of people will go "oh geez, here goes Therumancer on China again", one thought that did occur to me was a lot of old discussions about Chinese sleeper cells in the US, similar to a lot of old theories about the USSR during The Cold War which inspired movies like the old Kevin Costner vehicle "No Way Out". Given that Leland Yee was born in China, and is supplying weapons to a Chinese criminal/subversive organization it does make me wonder if his motivation here was entirely financial. It occurs to me that there would probably be better ways for him to make money illegally, with less risk or attention, say if he was brokering deals for weapons with both the source and the client being overseas (like a lot of other alleged government corruption, oftentimes theoretically tied to groups like the CIA).
That said, I'm curious how much we're going to hear about this trial. Given his high position in the government and access to classified information, the international nature of the crimes, the involvement of a known terrorist organization operating in a US territory (according to his wiki page), and the fact that he was trafficking not only assault rifles but missile launchers (again according to his Wikipedia page) he seems like a perfect candidate for a "spy court" and to spend the rest of his life in some deep dark hole, or a camp like Gitmo.
Of course at the same time, the big question becomes who he can give to the USA in terms of cutting a deal, which is going to be a factor (and again why it won't be in the public eye). Truthfully I'm a little shocked that this was put out publically the way it was, I would have expected the CIA and Secret Service (as he's federal) to grab him before
any announcement and pump him for a deal before an announcement, after all if they are going to use him to nail high end targets on both ends of his business you wouldn't want them to know they got something on Mr. Yee until after the fact when he's already turned all of his associates over. I'm not a huge fan of cutting deals with criminals, but it occurs to me that trading one corrupt senator for wiping out an entire terrorist organization in our territory and taking down the leadership of what is a 165 year old criminal organization (totally omitting any questions of intelligence involvement) would have been the smart play given what they seem to have on this guy.