If you have studied high school chemistry, you can probably guess that the so-called rotten egg smell should be the smell of hydrogen sulfide. Lu Zheng frowned and thought, what on earth would have the smell of hydrogen sulfide? Lu Zheng regretted that he studied liberal arts. He only remembered that hydrogen sulfide smelled like rotten eggs, but he didn't remember the basic characteristics of hydrogen sulfide at all.

He paced back and forth, and suddenly a light bulb went off in his head: "Oil!"

He remembered that he seemed to have read similar literature before. Crude oil contains petroleum gas, benzene, aromatic hydrocarbons and hydrogen sulfide, which are toxic to humans and other organisms. When the critical threshold of poisoning is reached, it will cause poisoning to humans and animals. The smell of hydrogen sulfide in crude oil is very likely what the two girls smelled.

Qingluan looked at Lu Zheng in confusion: "Master Lu, what are you talking about? Oil? Could it be oil produced in rocks?"

"That's right!" Lu Zheng couldn't contain his excitement, "The murderer is very likely to have used oil to set the fire."

"Then... where should we look for this... oil?"

Qingluan's words were like a bucket of cold water splashed on Lu Zheng's head. Even if he had no common sense, he knew that oil would not appear on the surface by itself. Generally, there would be a small amount of oil seeping out of the rock surface due to geological disasters or something like that. Lu Zheng was neither a geologist nor a chemist. He had no idea what the topography of the oil field looked like. How could he find it?

They said goodbye and left this family, and came to the widow's house again. Perhaps because Doctor Wang was traveling with them this time, the widow let them in.

This was a leaky thatched house, but it was much better than the thatched house of the previous family. Not far from this thatched house was their burned house.

In the small courtyard, a small stove was boiling Chinese medicine, and in the inner room was the widow's only daughter, who could only be heard coughing once or twice.

The widow looked sad and sighed, "I am a woman and I never go out of the house on weekdays. How could I make enemies with anyone?"

Doctor Wang comforted her, "At least the survivors are not injured. You just rest and don't worry."

On the second day after the fire, the widow's daughter began to cough and vomit. It was Doctor Wang who diagnosed her. At that time, Doctor Wang thought that they were not careful when using the charcoal brazier and did not think much about it. Now, after hearing what Lu Zheng said, he really felt the horror.

Lu Zheng did not sit down, but walked around and looked around. Suddenly he asked the widow, "Sister-in-law, is your daughter looking for a man?"

The widow was speechless and said, "Yes...Yes, how did you know?"

Lu Zheng actually found out when he saw the clothes that the widow hung in the yard. It was a new pink skirt. It didn't look like the widow herself was wearing it. It must belong to her daughter. Lu Zheng knew that for ordinary people, new clothes were usually made only during the Chinese New Year, let alone for a widow like this. It was probably because her daughter was just coming of age, so she made new clothes for the purpose of looking for a man.

Lu Zheng couldn't say it directly, so he could only fool around with ambiguity and asked, "Did anything strange happen in the days before and after the fire?"

The widow shook her head and said, "Nothing strange. My daughter and I have been embroidering at home. Except for some rice and flour sent by the clan, we have not seen outsiders."

Lu Zheng nodded and said, "Thank you for your help, sister-in-law. If you have any questions in the future, I hope you will tell me."

The widow also knew that he came to solve the case. She hated the arsonist in her heart, and immediately agreed, "Don't worry, sir. If you have any questions, I will tell you everything I know."

After leaving these two families, Lu Zheng suggested going to another family. This one was a bit far, but if they made good use of their time, they could still come back before sunset.

Without further ado, the three of them immediately headed towards that family. Compared to the conditions of the first two families, this one was obviously much worse. This was a family of four, and the head of the family was also surnamed Zhang. Doctor Wang called him Zhang Shitou.

Zhang Shitou had an old blind mother. His wife ran away because she thought life was too hard, leaving Zhang Shitou alone to raise a pair of children. The family only had one pair of pants, because the thatched house they originally lived in had been burned down long ago,

so they only built a straw hut to live in. Zhang Shitou's family was the first to be burned. Although it had been more than a month, Zhang Shitou still looked pale and his hands and feet trembled when he recalled it.

Seeing Lu Zheng and the others asking, tears immediately flowed down Zhang Shitou's face: "This...someone is trying to harm us! The Lord of Heaven must stand up for the common people!"

The three of them were cheered up at the same time. This was the first time someone directly said that the fire was man-made. Lu Zheng hurriedly asked: "Then did you see what the murderer looked like?"

Zhang Shitou wiped his tears and shook his head: "I saw...I saw it, but...but I didn't see it clearly..."

Although Lu Zheng was a little disappointed, he quickly cheered up. No matter what, this was a clue. He said, "Tell me exactly what happened that night."

Zhang Shitou rubbed his hands awkwardly, then whispered, "That night... I helped my mother wash her feet and poured out the water... My mother said she wanted to eat eggs... I... I was incompetent. Not only did I lose my wife, but my mother couldn't even eat an egg she wanted. I..."

Seeing that Zhang Shitou was about to cry, Lu Zheng could not help asking, "What happened next?"

Zhang Shitou wiped his tears, sniffed, and then continued, "Later... Later I rubbed mud into an egg-like shape for my mother to touch, and lied to her that she could only eat it the next morning... My mother believed it. , I... I slept with the child... Although my mother is blind, she has good hearing. In the middle of the night, she suddenly pushed me and said that the eggs were cooked and asked me to go and see... I opened the door in a daze, and saw a shadow lying on our haystack... I... I thought it was a wolf and was trembling with fear. Then... that person jumped down from the haystack, and then... then he set a fire in our yard... I..."

Although Zhang Shitou spoke intermittently and incoherently, Lu Zheng and the others still understood. Qingluan asked quickly: "Do you smell anything?"

Zhang Shitou touched his head blankly: "No... no..."

"Nothing?" Qingluan pressed, "Like the smell of rotten eggs?"

Zhang Shitou shook his head repeatedly: "No, nothing."

Qingluan seemed a little disappointed, but Lu Zheng had a sense of reason. In fact, for serial killers, their psychology will slowly transition from fear and tension to excitement at the beginning, and in this process, their methods of committing crimes are constantly upgraded. For example, the first case Lu Zheng encountered here, the prisoner Zhang Hu also constantly upgraded his methods of committing crimes again and again, from peeling the skin after death to peeling the skin while the person is alive, and even later he would fold the clothes of the dead neatly aside, which also shows that his mentality has become enjoyment.

Arson is a relatively easier method for arsonists to commit crimes than direct murder, so the general profile of arsonists is that they are introverted, timid, and mentally retarded, and many even have physical defects. They vent their dissatisfaction with life by committing crimes against innocent people to balance their inner anger and jealousy. For

any serial case, the first case is very valuable. So Lu Zheng asked Zhang Shitou: "Have you ever made enemies with anyone?"

Zhang Shitou was at a loss for a long time before he managed to utter: "Tian Fugui, he...he was the one who kidnapped my wife..."

Lu Zheng looked at Doctor Wang in confusion, and Doctor Wang sighed and said: "This Tian Fugui was originally a young man in the village. He disappeared with Zhang Shitou's family a few years ago. It was said that the two of them eloped..."

"It wasn't an elopement! It was Tian Fugui who abducted my wife!" Zhang Shitou stood up excitedly, gesticulating as he spoke, "My wife is a good woman, she wouldn't elope... She was abducted..."

After that, Zhang Shitou kept repeating this sentence in his muttered voice and didn't come up with any useful clues. Lu Zheng sighed and asked Doctor Wang, "Where is Tian Fugui's home?" Although he felt that Zhang Shitou's words were useless, it was still a clue after all.

Doctor Wang said, "It's not far. We'll be there in a little while if we go there."

On the way, Doctor Wang told Lu Zheng about the Tian family: "The Tian family moved into our village later. There are not many of them, only seven or eight households. However, the girls in the village are unwilling to marry them, so they either find a wife from other villages or several brothers share one wife."

Lu Zheng's eyes widened: "How can this be possible?!"

Doctor Wang sighed . "Sir, you have seen that here, there are more men than women. To marry a wife, even a family with a lot of money will have to spend most of their money. If the girl is pretty, they would rather marry her in the county. Take the family of Wang Youli that we visited earlier. His daughter was originally going to marry the son of a shopkeeper in the county, but now their family has burned everything, not to mention the dowry, even the lottery ticket. The gift is gone, and the shopkeeper has changed his mind and said that he will not marry her and let them pay for it. But even so, as long as the girl agrees, there are many people in the surrounding area who want to pay to marry her." He paused, glanced carefully at Qingluan beside him, and said, "It's okay here. If we go further north, the girls will all marry soldiers of the Northern Frontier Army, and it will be even more difficult to find a wife."

Qingluan glared at him and said, "What nonsense are you talking about? "It's as if it's our Northern Frontier Army that prevents them from getting married. If they have the ability, there will naturally be girls willing to marry them. It's unreasonable for them to blame others for their own incompetence!"

In fact, what Doctor Wang said was not bad. The Great Xia Dynasty was not stingy with its soldiers, not to mention the elite soldiers among the elite soldiers such as the Northern Frontier Army. Compared with farmers who face the loess and back to the sky, there are indeed many girls willing to marry soldiers.

Doctor Wang just thought about these words in his heart, and smiled and agreed: "This young man is right." Then he said, "Look at me, what have I talked about now? Oh... Let's talk about Tian Fugui. His family has three sons, and none of them are married. Tian Fugui has evil thoughts. In his early years in the village, he liked to peek at girls and wives taking baths. Later, I don't know how he hooked up with Zhang Shitou's family... Oh, look, that's Tian Fugui's family."

Lu Zheng and Qingluan looked over as Doctor Wang instructed, and saw a row of messy fences, and behind the fences was a burned house.