As for whether Wesker was a traitor, everyone had found it unbelievable at first. But Rebecca soon confirmed it. According to her, after separating from Fang Zheng, she, Emma, and Laura had followed the train maintenance passage to a rather ancient-looking building. Based on the fragments of information they had found there, it seemed to be a place Umbrella Corporation used to train its employees.
Of course, that was not the important part. The important thing was that, prompted by Fang Zheng, Rebecca remembered that the note she had found by chance did indeed contain the names William and Wesker!
She had not thought much of it at the time, but after hearing Fang Zheng say that, Rebecca immediately grew suspicious.
Could the Wesker on that note have been the Captain of their S.T.A.R.S. team?
So she said she would continue searching the place to see if she could find evidence proving it. At the same time, she told Fang Zheng that the place had also been infected by the virus, and everyone had turned into zombies—well, that was within Fang Zheng's expectations.
Fang Zheng also suggested that Rebecca take Laura and Emma to the mansion to rendezvous with them. The situation before them had far exceeded what a single squad could handle. Fang Zheng would rather get everyone safely back to Raccoon City, report to their superiors, and let people at a higher level deal with the matter... Well, the police chief was out of the question, of course.
That was right, Fang Zheng's idea was—if he could not stop the game from being solved, then he could simply go around it!
In the game, after the S.T.A.R.S. members had been lured to the mansion, the most prudent course of action would actually have been to hold their ground