Purim thoughts

Everyone nows that Achashveirosh did not know where Esther came from. What is interesting is that the gemara in Megillah says that Esther would leave Achashveirosh, go toveil and go to be with Mordechai.Now Esther was in the palace for 9 years before the end of the story. You would have to assume that Achahsveirosh had his best men working to find out where Esther came from. I would assume that would include keeping tabs on her and seeing who she was in contact with. Yet no one was able to catch her sneaking out to visist Mordechai. I find this very interesting.