If Chan Wing-yan hadn't left the folder exposed on the table and left Lau Kin-ming's office, he could probably have gotten his identity as a cop back and then expose Lau Kin-ming to the higher authorities. Just my 2 cents.
shareI was wondering about this as well. As soon as he discovers that Lau is the mole, Chan just takes off. Then later he has to blackmail Lau to get his identity back. If he had just stayed put, wouldn't he be able to get his life back? Or perhaps he was worried about what Lau would do to him now that they've seen each other?
shareI thought that he was worried what Lau would do now that he had him safe at the precinct. He had no way of knowing that Lau was not going to turn him in and erase his files at that time.
shareIt's six of one; half a dozen of the other isn't it?
I agree though. He hadn't been in a police station (as an officer) for 10 years and couldn't really predict what Ming might do or have on him.