I, from the Celestial Empire, have parachuted into Teyvat.

After listening to Song Ke's description of the case, Ivan turned around and nodded to Zheng Yuan and his group.

"Brother Zheng, from now on, I'll be relying on you."

Zheng Yuan said, "Hey, no trouble at all. This is our job anyway. Leave the rest to us."

After Zheng Yuan finished speaking, the others quickly unloaded the tin boxes and packages from the carriage and carried them into Ma Sanshui's courtyard.

Watching Zheng Yuan and the others' actions, Ke Qing, who had been filled with curiosity, finally couldn't help but ask, "Mr. Ivan, what's going on with your friends?"

Ivan smiled and kept everyone in suspense.

"Don't ask yet, you'll find out soon enough."

Chapter 117 Modern Criminal Investigation Methods

As the investigation began, Zheng Yuan and his group carried all the large and small metal boxes into the yard.

Ivan Keqing and the others observed carefully from the side, especially Keqing and Song Ke, who were curious about what was inside the packages and boxes.

Zheng Yuan quickly answered the question.

I opened a bag, inside were rubber gloves, a mask, and some small tools.

Zheng Yuan quickly put on a pair of gloves and a mask, and the others did the same. This scene puzzled Ke Qing.

What are we supposed to do?

Zheng Yuan didn't say anything, then opened the second box and took out a professional camera.

Keqing blinked and said, "This thing looks familiar... Is it a phonograph from Fontainebleau?"

Ivan explained, "The principle is similar, but this is much more advanced than the phonograph machine in Fontainebleau."

At this moment, a woman wearing glasses from Zheng Yuan's team walked up to Song Ke with a bottle of liquid and what looked like a roll of test strips in her hand.

"Have you been the only one to have entered and exited this site so far?"

Song Ke was taken aback for a moment: "I guess so. From the time someone reported the case to when I came to investigate, I was the only one who came in."

The woman nodded and said, "Extend your hand."

Song Ke was a little confused, but he still did as instructed.

"Palm up."

"Forehead."

Song Ke turned his palm over, and the woman applied the liquid from the bottle in her hand to the pads of Song Ke's ten fingers, then pressed a test strip onto each finger one by one.

"All right."

After doing all that, the other person left.

Ke Qing asked curiously, "What are you doing?"

Ivan said, "We are taking fingerprints."

After saying that, Ivan extended his hand, palm facing Keqing.

"Fingerprints are amazing things. Because everyone's genetics and growth environment are different, everyone's fingerprints are different. The probability of repetition is extremely small, only about one in 150 billion. This probability is basically equivalent to not repeating. Therefore, fingerprints are like everyone's ID card. Every pore on the human body has sweat glands. In daily life, no matter what you do, as long as you touch something with your hand, you will definitely leave fingerprints on it."

"We are taking Brother Song's fingerprints to avoid mixing up other people's fingerprints with his when we take fingerprints from the scene later."

Ke Qing nodded in sudden realization, finding it even more amazing.

Ke Qing asked, "So, Mr. Ivan, all the people you invited are detective experts from China?"

Ivan smiled and said, "To be precise, they should be called criminal investigation experts. Dr. Zheng Yuan's team has solved countless cases in China, and almost no criminal can escape their pursuit. If you are interested in criminal investigation, I can take you to visit China sometime."

Keqing did not refuse and nodded, which was considered as agreeing to Ivan's request.

Meanwhile, Song Ke's matter was not over yet. Another member of Zheng Yuan's team came over and made a rubbing of Song Ke's footprints. Similarly, Ivan Keqing and Xiang Feng, who had entered the courtyard, did the same.

This is done in the same way as fingerprints, to avoid confusion with the footprints of key figures in the case.

Zheng Yuan's team had a clear division of labor: half of the team went into the crime scene with tools to investigate, while the other half opened all the metal boxes outside.

At this moment, the true contents of all the items inside these metal boxes were fully revealed to Ivan and the others.

These are portable laboratory workbenches and various portable laboratory analytical instruments.

The general procedure for criminal investigation is that after criminal investigators investigate and collect evidence at the crime scene, the evidence is handed over to the laboratory for further analysis.

However, since everyone is currently in Teyvat, the conditions do not allow them to collect evidence here and then bring the evidence back to Earth for testing and investigation. In order to save time, they simply moved the entire laboratory here.

Ivan explained the functions and uses of all these things to Keqing. Looking at these strange and wonderful devices, Keqing's curiosity intensified, which strengthened her resolve to go to China to see for herself.

After investigating, Zheng Yuan walked up to Ivan and asked, "Commander Ivan, are there other families in this village whose members have gone missing?"

Ivan nodded: "Yes."

Zheng Yuan said, "Then let's go and take a look at the other ones."

Soon, after half a day, the evidence collection for all the missing persons' families was completed, and the evidence was taken to the testing table and handed over to the team's professionals for testing.

Since Ivan and the others couldn't offer any help, they sat quietly to the side and waited.

A short while later, Zheng Yuan came over with an investigation report and handed it to Ivan.

Ivan took the document and glanced at it, then exclaimed in surprise, "Besides the missing person's fingerprints, footprints, and other people who had been at the crime scene, there's nothing else found?"

Zheng Yuan nodded and said, "We investigated every corner. Take Ma Sanshui's house as an example. The fingerprints extracted from the pots, pans and other daily necessities found at the scene show that Ma Sanshui was indeed alone at home when he disappeared. This is really strange, because according to this conclusion, Ma Sanshui could only have left on his own."

Ivan frowned: "Is there any way to continue the investigation?"

Zheng Yuan smiled and said, "Commander Yi, don't worry, we're far from being powerless. In any serial case, there will always be similarities between the victims. We just haven't found any similarities yet, and we need to conduct further investigations. In addition, there is still a need to further investigate the crime scenes."

After hearing Zheng Yuan's words, Song Ke asked with some doubt, "Is there really any need for further investigation at the crime scene? I'm not trying to belittle or look down on you, but I think since your investigation results are the same as mine before—no clues were found at the scene—there's no need to keep lingering at the crime scene. Isn't that just a waste of time?"

Faced with Song Ke's questioning, Zheng Yuan was not angry, but smiled and said, "Sir, have you heard of Locar's law of exchange of matter?"

Song Ke looked puzzled: "Lokar what?"

"Locard's Law of Exchange of Matter".

Zheng Yuan explained: "Locar's law of exchange of matter states that as long as a criminal commits a crime, he will inevitably act directly or indirectly on the victim and its surrounding environment at the crime scene, leaving traces consciously or unconsciously. These traces can be categorized into three types: the first is physical traces, such as fingerprints, footprints, crime tools, bodily fluids, etc.; the second is perceptual traces, such as traces left by someone who witnessed the crime scene; the third is psychological traces, where the suspect commits the crime for a certain purpose or with a certain mentality, even if it is an impromptu act, there is still a process of mental activity involved."

"There can never be a perfect crime in the world."

Chapter 118 Target: Jueyun Pavilion

Zheng Yuan's theoretical explanation greatly benefited Song Ke, who then fell into deep thought.

Seeing Song Ke's thoughtful expression, Ivan knew that his investigative skills would likely improve significantly, which would pave the way for his future promotion.

"You Chinese are really interesting; you actually managed to come up with such a theory."

Ke Qing sighed, her interest in China growing even stronger.

Ivan smiled but didn't say anything.

Keqing is the ruler of Yuheng Star in Liyue, responsible for Liyue's civil engineering and public administration. In this regard, whether on Earth or Teyvat, China is second to none, being a super-infrastructure powerhouse. When Keqing goes to China in the future, she could perhaps study infrastructure-related knowledge there rather than criminal investigation.

Having decided to conduct an in-depth investigation, Zheng Yuan's team immediately began to take action.

First, Ivan and his team moved to the outside of Ma Sanshui's courtyard wall to cooperate with the work. Then, Zheng Yuan and his team began to take samples of the microscopic evidence at the scene using chemical equipment such as test tubes. Because this sampling work might damage the integrity of the scene, Zheng Yuan had already taken videos and photos of the scene in advance.

Zheng Yuan's team acted quickly, extracting soil, dust from objects, and even air from the site and taking it to the laboratory for testing. The results came back quickly, and as before, there were no useful findings.

Zheng Yuan frowned. If no evidence could be found at the micro level to prove that anyone other than the missing person had come, then it meant that the missing person had indeed gone out on his own. Could it be that someone was standing outside calling him?

After thinking for a moment, Zheng Yuan called out, "Su Yang."

A middle-aged man who was watching the testing process at the lab table looked up.

"Boss, what's wrong?"

"Come here."

Su Yang walked up to Zheng Yuan, who squinted and said, "No trace of a second person was found at the scene, which means that no one else came here except for the missing person. I want to know how the missing person left on their own."

Su Yang nodded, took out a notebook, and began to observe and record things at various locations around the scene.

Outside the courtyard, Ke Qing asked with some curiosity, "What are you doing?"

Zheng Yuan walked over and explained, "Su Yang is the only profiler in our team. He's reconstructing the scene when the missing person left."

Ke Qing raised an eyebrow: "Can this thing be restored?"

Ivan smiled and said, "Criminal profiling starts from a psychological perspective. By analyzing the things at the scene, it infers what happened there, and then further analyzes the psychological activities of ordinary people or victims. Finally, it summarizes the criminal's behavior habits and personality, as well as their identity, environment, and upbringing. Of course, this time we know the background and circumstances of the missing person. This is just a simple deduction of the scene when the person left, which is not too difficult."

Soon, Su Yang came over with a notebook full of notes.

"Boss, the analysis is almost complete."

Zheng Yuan nodded: "Yes, how is it?"

Ivan also came over out of curiosity. Although he had seen many criminal profiling plots in TV dramas, this was the first time he had seen one in real life, and it was quite novel to him.

Unlike most TV dramas where the profiler closes their eyes and mentally analyzes the target's activities while performing, which is artistic embellishment and somewhat detached from reality, Su Yang simply and plainly recorded everything he observed around him in his notebook. Finally, based on these records, his knowledge, and years of experience, he listed out the most likely behaviors of the target, just like writing a mathematical proof.

Su Yang said, "Based on my analysis, Ma Sanshui should have been at home preparing a meal when he disappeared. This can be seen from the placement of the pots and pans and the signs of use. He was probably washing a pot, but then he suddenly stopped what he was doing, turned around, and walked towards the door. He even brushed against the dust on the door frame. He wasn't walking fast; in fact, he walked very slowly. But there were no walking aids or signs of leg problems in Ma Sanshui's house, so his legs were fine. I previously suspected that someone was calling him from outside, but if an ordinary person heard someone calling them, they would rush out to see what was happening. Ma Sanshui's slow pace was obviously unreasonable, so I ruled out this possibility. The second possibility is that he suddenly remembered something and went out, but the situation is the same as above; his speed was too unreasonable, so that was also ruled out. Now, only the third possibility remains: he was hypnotized."

"Hypnosis?"

Ivan raised an eyebrow. He suddenly recalled a scene from the original game's storyline where the little girl, an incarnation of the Dragon King Rota, hypnotized and controlled several miners to dig at the location of his seal in order to break it. This was Rota's ability. He then recalled what the young master's confidant had said earlier—that the little girl who spoke with the lady was accompanied by many men, women, and children, and that they were behaving in a dazed and confused manner…

The situation is quite clear: these disappearances were likely committed by the Naga King Ratna.

But a new question arises: where did the Dragon King Ratna exert hypnotic control over these people?

Just then, a female member of Zheng Yuan's team, who had previously gone out to investigate commonalities among the missing persons, rushed back in a hurry.

"found it!"

Zheng Yuan exclaimed in surprise, "You've found something in common?"

The woman nodded, took out the investigation report, and said, "I visited all the homes of the missing persons and also went to the homes of missing persons in several nearby villages to investigate. In the end, I found that all of these missing persons had intentionally or unintentionally gone to or passed through a place called Hulao Mountain within a month."

"Mount Hulao!?"

Ivan's face showed surprise and doubt. He remembered that Mount Hulao was home to Liyue's Immortal Lord, the Water-Climbing Mountain Master, and Mount Hulao was adjacent to the South Heavenly Gate, the place where the Dragon King Ruoduo was previously sealed.

After the Emperor's "death," all the immortals and the Seven Stars came to find Ivan, including the True Lord of Lishui Dieshan. Ivan also told the True Lord of Lishui Dieshan about some demon gods hiding. The True Lord of Lishui Dieshan agreed at the time. However, later, when Ivan was chatting with the True Lord of Liuyun Jiefeng, he heard that the True Lord of Lishui Dieshan had been in seclusion in his cave recently and had not gone out.