Maid Lotus had been quickly taken off the suspect list. The prostitute had seen a "long-haired ghost" who was very likely female, while several other people had seen Maid Lotus bumping into and nearly fighting against said "ghost". Therefore it was impossible for her to have been Wu Ling's murderer.
As a matter of fact, the killers waiting outside had initially suspected Maid Lotus when they were unable to catch the assassin. They quickly realized though, that this was false.
In Golden Roc Fort, most apprentices would not grieve when their mentors were killed.
Mentors, in general, did not treat their apprentices as humans. During times of relative peace and little carnage, those with many apprentices would force them to engage in fights to the death, so as to quickly eliminate the weaker ones. Cases of torturing or raping their apprentices were even more common. The mentors not only received no punishment but would brag about their deeds among themselves.