Which teen horror mystery novel series was released around 2004?

Around 2004, he remembered that there was a series of mystery novels called Shonen Thriller Mystery. Each book was very thin and had a white cover, but there was a green skull in the upper right corner (or upper left corner). One of the stories was about a child, and the final reason was that they were twins.
Please ask for the title!
It was a detective novel, the kind that was written purely in words…It was not Conan. But it seemed to be Japanese.

Answer 1

"It might not meet your needs, but I would like to recommend a novel that is most relevant to your description of your needs. The book, Folk Taboo, is a suspense-mystery detective novel written by a scholar. The general plot of this novel is as follows:

What kind of horrifying events were hidden behind them? After experiencing several life and death situations, the young and frivolous me...
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"The Strange Case" was a suspense-mystery detective novel written by the author, Wu Jian Wen. The general plot of this novel was:

Truth and falsehood, truth and falsehood, inaction, existence and nothingness, searching for the truth in the fog. Little brothers, this is my first time writing a novel. I'm a newbie, O(headquarter)O.
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"Miss Detective of Criminal Investigation" was a mystery detective novel written by the author, Jianli. The general plot of the novel was:

Looking for the truth in the fog,
Looking for the murderer in the midst of danger,
Live for the truth, die for the truth.
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"Strange Detective Firm" was a suspense-mystery detective novel written by Ming Shaosi. The general plot of the novel was:

In the peaceful and quiet city, there was a demon-like existence. Behind the murder cases, was there a true feeling or a strange groping? With a righteous mission, he investigated these mysteries and found the truth hidden in the depths.
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"The Death of the Detective" was a suspense-mystery detective novel written by the author, KY. The general plot of the novel was:

Sophomore student Mo Li's case solving story, the first case was a secret room incident, and then encountered a moving coffin case. Faced with a series of secret room incidents, a series of suspicious events, detective Mo Li opened the layers of fog and arrived at the truth.
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"My Years as a Ghost Detective" was a suspense novel written by Detective Yu Shi. The general plot of the novel was:

The Heavenly Dao had a constant, the cycle of life and death. However, there were always some people who died unjustly. After death, they would have deep resentment and turn into evil entities. They would not enter the cycle of reincarnation and would wander the human world. And I am the one who helped them find out the cause of death, resolve their grievances, and enter the path of reincarnation. What I'm going to talk about next is the various hair-raising things that I've encountered as a detective over the years. Detective-Xue Shaobai.
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Time Detective was a mystery detective novel written by Dancing Rain Song. The general plot of the novel was:

The teenage girl had her throat slit for no reason, but she was unexpectedly reborn in the body of a female traffic policeman. He had also obtained a magical ability! In order to find the murderer, the girl joined the criminal police team and solved many strange cases!
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"Picking Up Doubts" was a suspense-mystery detective novel written by the author, Sui Liang. The general plot of this novel was:

In 2002, a murder occurred in a villa in Daoyuan County. A young girl was killed. The identity of the murderer was unknown until it became an unsolved case. In 2012, the magazine editor, He Liang, took a mysterious photo with his father's camera. The case was confusing, but where was the truth? Pick up the questions and you will know.
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"Treacherous Heart Panic" was a suspense novel written by the author, Triste Wenhao. The general plot of this novel was:

This article presents 17 different types of medium-length stories, including suspense, supernatural, sci-fi, mutation, military, urban, ancient costume, doujin, transmigration, adventure, spiritual reconnaissance, and other different styles. It vividly portrays each bizarre story in detail!
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"My Years in the Major Crimes Division" was an urban supernatural novel written by Rookie Old Qiang. The general plot of the novel was:

Ren Tianya, who had transmigrated into the Key Case Investigation Unit, had the Super Detective System.
From then on, he began his detective career in solving all kinds of strange and important cases…