When Lu Zheng heard the guard's voice, he rushed over immediately and found that in front of him was a rock with black oil oozing out. The expressions of the villagers present were all suspicious, and even the originally calm guards were talking about it.

Lu Zheng dipped a little with a sweat towel and put it under his nose to smell it. Sure enough, he smelled the familiar smell of gasoline and a pungent odor. Although he had never seen crude oil, he could guess that this was most likely crude oil. He stopped hesitating and quickly asked people to go inside.

They hadn't walked far when they gradually smelled a stronger and stronger pungent smell. The two villagers were unwilling to go inside no matter what, and Lu Zheng understood. After all, it is a common problem for humans to be timid about things that they are not familiar with. The rest of the people continued to walk inside.

If we must describe the shape of this mountain, it is very much like a ladder, narrow at the top and wide at the bottom, but the top is slightly concave inward, forming a landform similar to a basin.

Lu Zheng and his team soon saw the scene in the heart of the mountain. There were no tall trees here, only some short shrubs and tenacious weeds. Black oil stains slowly slid down from the broken rocks, leaving a black mark, and in the center, there were even a few pits filled with black oil.

Lu Zheng's eyes widened in amazement. Even if he was poor at geography, he could tell that this was a rich oil field.

Doctor Wang took two steps forward, wanting to take a closer look, but was pulled back by Lu Zheng who reacted in time: "Doctor Wang, there may be toxic substances in the oil. It is better for you to cover your mouth and nose before taking a look."

Doctor Wang laughed and said, "Look at me, I'm not as calm as Mr. Lu."

Several people took up the masks that were made overnight. Lu Zheng had taken this situation into consideration at the time, so he specially asked someone to sew them. Now they really came in handy.

Li Zheng was obviously hesitant about the next action: "Master Lu, what exactly are these things? We haven't encountered any birds or other animals along the way. Are we all harmed by these things?"

Lu Zheng pondered for a moment before saying: "We haven't encountered any birds or animals. It is very likely because of the change in the environment. The soil layer on this mountain has cracked, so it is difficult for plants to grow. Animals have no food, so they will gradually leave here. But it should also be related to this oil. This oil contains a substance called hydrogen sulfide, which is poisonous. Maybe that's why the animals left the mountain."

"Even if the ban is lifted, it won't help the people in our village." Li Zheng seemed a little disappointed. One of the main reasons why he agreed to let Lu Zheng come to the back mountain was that he hoped to lift the ban again and give the villagers another way to make a living. But now there are no plants or animals in this mountain except for these poisonous oils. What's the use of it?

Lu Zheng shook his head: "Don't underestimate this oil, it has a great effect."

Because of time constraints, Lu Zheng couldn't conduct experiments on the spot. He asked several guards to fill cowhide water bags with crude oil and prepare to return to the station to conduct another experiment. Of course, the most important purpose of their trip was to find evidence related to the previous arson case, and Lu Zheng had not forgotten these, so while the guards were refueling, he circled around a few times.

Although he did not investigate very carefully, Lu Zheng soon found clues. The first was a footprint. Lu Zheng compared it with his own. His feet were not very big. If he changed to a shoe size of 40 in modern times, this footprint was smaller than his feet, which meant that this person was either a teenager who had not grown up yet, or was short, or a woman.

In addition to the footprints, Lu Zheng also found a rattan backpack behind a rock. In the backpack was a rotten sweat towel and some wooden dolls. Lu Zheng took out the dolls and saw that they were crudely carved, with big heads and small bodies. They did not look cute, but rather uncoordinated and mysterious. The expressions on the faces of the dolls were different, and one could even barely tell the genders by their hairstyles.

Lu Zheng took out all the dolls and laid them out on the ground in parallel. There were a total of nine dolls. The first doll was a laughing man with a straw scarf-like thing on its neck. The second doll was a woman with no nose or mouth, only a pair of eyes much larger than those of an ordinary person. Compared to the first doll, this doll was obviously more carefully made, because it not only had hair glued on its head, but also wore clothes made of sweat towels. The remaining dolls were similar to these two.

After Lu Zheng looked around, he found that these dolls had no gender characteristics. The difference between men and women was the clothes and hairstyles. Men basically had no hair, while women had relatively delicate hairstyles.

Lu Zheng suddenly seemed to have thought of something and rearranged the dolls. Now the first doll had a sad face and a big hunchback on his back. Lu Zheng remembered the first family that caught fire, Zhang Shitou, who was a bit hunchbacked, and the second one was the woman without a nose and mouth, and the second one was the widow's house, the widow only opened the door a little, revealing only her eyes. As for the last puppet, it was the first one Lu Zheng held in his hand, the puppet with a sweat towel around its neck.

The name Niu Da jumped into Lu Zheng's mind.

If these puppets belonged to the murderer, then these puppets were the real reason why he set fire. He set fire to the posthouse not because he had a grudge against Zhang Lin, but because of the postman Niu Da.

With this discovery, Lu Zheng carefully wrapped all the puppets with handkerchiefs and put them in the backpack behind him. At this time, the guards had already loaded the crude oil and were ready to set off back.

Doctor Wang came over with a serious expression: "Mr. Lu, have you found any clues?"

Lu Zheng then told him about his discovery of the dolls, and added: "I don't know the families whose houses were on fire, so I may have to trouble Doctor Wang for help later."

Doctor Wang nodded: "Of course, it's my duty." Li Zheng

had been frowning on the way back. He took the risk to lift the mountain closure order, hoping to give the villagers another way to make a living, but he and Doctor Wang couldn't figure it out. Lu Zheng refused to explain the use of the oil, and he didn't know how to explain it to the villagers and the elderly in the village.

Lu Zheng didn't know what to say. After all, it was an era when the steam engine hadn't been invented yet. Even if he knew the concept of a gasoline engine, he wouldn't be able to make one. Even if he said it, it would be useless. It would only make Li Zheng happy for nothing. Now that these crude oils have been discovered, in addition to finding the arsonist, the rest depends on whether they can help the battle in the northern border.

Back at the villa, Rong Zhen had been waiting for a long time. Seeing that Lu Zheng was not injured except for some dirt and grass on his body, he was relieved and asked, "How is it? Did you gain anything?"

Lu Zheng nodded, took out the puppet wrapped in a handkerchief and put it on the table.

Doctor Wang has always been a casual person, but when he really saw the King of Chu in person, he unconsciously felt a little weak in the legs and was much more reserved in his etiquette.

Lu Zheng was now concentrating on his work. Seeing this, he quickly pulled Doctor Wang over and pointed at the dolls on the table and said, "Doctor Wang, could you please identify whether these dolls represent the people whose homes were set on fire?"

Doctor Wang frowned when he saw the puppet. Although he was a doctor, Chinese medicine emphasizes observation, smell, questioning and palpation, among which observation is a very important aspect. Observation is not only about looking at a person's complexion and superficial symptoms, but also about some things related to metaphysics. For example, in ancient China, there were powerful Chinese doctors who could tell what disease a person had by looking at his handwriting. Of course, many times this is just a feeling, which requires doctors to have very rich experience.

Doctor Wang felt very uncomfortable when he saw the puppet for the first time. If he hadn't been helping Lu Zheng solve the case, he would have destroyed these puppets long ago.

Doctor Wang quickly identified all the puppets and sorted them out, with one puppet corresponding to a fire. When he came out, he was stunned, especially when he held the puppet wearing a sweat towel, his hands were shaking.

"Master Lu, this..."

Lu Zheng nodded solemnly: "This should be carved by the murderer."

These puppets make people feel uncomfortable, and puppets are generally related to witchcraft or curses in ancient China, which means that the murderer hates the prototypes of these puppets. According to some characteristics of arsonists that Lu Zheng learned, these people generally have extreme resentment and anger towards society, and they are introverted, timid, and accompanied by physical defects or low intelligence. They cannot vent this resentment, so they use arson, which does not require much technical content and physical requirements, to vent their resentment towards others.

The murderer did not choose to set fire indiscriminately. On the contrary, he had a purpose for the family that set the fire. He was not satisfied with just setting fire directly, which was a matter of no technical content. Instead, he used crude oil to help the fire. At least this showed that the murderer was not mentally retarded. Moreover, he could often go in and out of the back mountain, so his limbs should be fine. But in addition to this, using puppets to express resentment is generally a common method used by children or women. So, could it be that the perpetrator was a child or a woman?

This is somewhat consistent with the footprint that Lu Zheng had seen before, but even though the information about the murderer had been found, everyone's expressions did not ease up.

The reason was that in addition to the puppets that Doctor Wang had placed, there was another puppet left on the table.