What are the symptoms of that mental problem?
How can you read the symptoms?
How can you determine that this particular individual is having those symptoms?
Is this a hereditary disease?
How many such patients are now in China?
What age they represent in average?
What will be the treatment?
Will they be experimented in laboratories?
Is there any drug that can cure such disease?
Or will they be executed?
I know, you can't answer these questions.
What you are suggesting to do will be like witch hunting that occurred in medieval Europe and continues to occur in Africa and even India. This will create further social problems. Suppose, a guy is having problem with another guy, the former will try to accuse the latter of being mentally unstable and if by chance locals get convinced, authorities will hunt down the innocent man and execute him. Thus, an innocent man will be victim of social paranoia.
Fear will prevail in the society and everyone will suspect his neighbors of having such mental disease. In the remote rural areas, people will take laws in their hands and will start killing people saying they were psychos.
If you study the recent cases, as far as media reports are concerned, you will find the criminals' excuses were not similar. The marital status of criminals for all cases are not similar. They don't belong to the same age. Though, I don't know about their records in family lives and their locality.
Symptoms are not always obvious, especially because people with such mental disorders tend to be asocial, which decreases the chances of people noticing his illness. Generally, these people are considered simply "weird". You need to understand that there is no "schoolyard rampage" illness. A whole plethora of mental illnesses, when severe enough, can cause something like this. Even among psychopaths there are huge differences. So it's impossible to answer such questions "how can they be treated" or "at what age do they present the symptoms" with authority. However, if you wish, I could look up some research papers for you to give you some educated guesses. It is, however, a fact that they're largely hereditary.
The truth is that not enough is done around the world and especially not in China regarding mental diseases. Hell, not too long ago China considered homosexuals as mentally ill!
As for my suggestion, what did I suggest? I suggested nothing. I don't believe that there's anything they can realistically do. I completely agree with you on the dangers of a Salem watch trial, which is why I said that "aggressive screening can cause a lot more problems", to paraphrase.