Si Nuo is the last big boss, and Dan is just his helper.
I am sure that Sinoe is the last big boss because 1. In the film, Qin Feng also made this guess, or affirmed it instead of guessing, because if it is not the truth of the reversal, it is not unnecessary to add this bridge for no reason.
Only in this way can it make sense and link the development of the whole case. Because everyone has seen Mr. Li working in an abandoned factory, it can be explained that Mr. Li is not a literate person and it is impossible to organize such a nearly perfect crime. The only possibility is that, as Qin Feng said, Mr. Li read the killing method in Sinoe's diary and executed it according to the killing method written in Sinoe's diary.
3. Snow's weird smile at last also proves this point, because Snow just smiled when he mentioned the sentence "Everyone is born to play the role of good and evil" and asked if the villains in Qin Feng should laugh like this. The doubt here is why Sino didn't show a kind smile according to her lovely and sweet style at first, but an evil bad smile, which also shows that she is the kind of person who wants to play evil, so it just shows that Sino is the murderer.
There is another place that also implies the fact that Sinoe is the last big boss, that is, the paper. Because a girl who can plan a perfect crime like Si Nuo can't solve this problem, it's a logical mistake after knowing the truth, so this paper combines the meaning of Si Nuo's words, that is, the distinction between good and evil is on the first line, between thoughts, which means that the meaning of this paper is to interpret the loveliness before Si Nuo and the evil after knowing the truth. In fact, this difference is only between this line. When Si Nuo asked Qin Feng this question, it was a hint to me.
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Another question is whether Sompa's son Dan is dead or not. The answer is-no, if Dan died, Si Nuo's perfect crime would not be so successful logically.
Why do you say that:
1. Dan and Si Nuo in the photo are so close that everyone guesses that they are boyfriend and girlfriend. As we all know, another thing about Sompa is homosexuality, and Dan must have been sexually harassed. Dan and Sinoe are in love and can't accept Sompa's "love". Dan knows Sinoe's ability and asks Sinoe for help. (It is also possible that Sompa is not Dan's biological father because it is unlikely that a gay man will have a baby with a woman, but it is not impossible, because we don't know whether Sompa was gay or had a baby with a woman from the beginning. On the other hand, Si Nuo also saw his adoptive father's inexplicable love for himself, and worried that his adoptive father would take some actions against Dan and separate himself from Dan, so he had such a near-perfect crime and murder.
2. In Si Nuo's diary, it was mentioned that he would enter Sompa's workshop before the surveillance video was covered. There is no doubt that Si Nuo's home is far from Sompa's workshop. It is theoretically impossible to know how many days the surveillance video will be automatically covered. Dan must tell Si Nuo that there is another possibility that all surveillance videos in Thailand are like this. Obviously, this possibility is not great.
The diary said that he would hide in Songpa's workshop one week in advance, but Songpa often went to the cafe, but the door of the workshop was locked. Since the lock is not broken (which will arouse Songpa's suspicion), how did Mr. Li get into Songpa's workshop? Obviously, Dan must provide the key.
4. How did Si Nuo know that Sompa would follow his classmates after Dan disappeared? Obviously, people familiar with Songpa told Si Nuo that the only person familiar with Songpa was Dan.
If Dan dies, logically, it is impossible for Sino to complete this almost perfect crime, so Dan just disappears, or is hidden by Sino.
That's why I'm sure Kano was the last big boss and Dan didn't die, so he became Kano's helper.