Through the relative query of the household registration database, Song Lang found out that He Jingjing's former name was Li Jingjing. Li Jingjing's father was Li Qiang, and Li Qiang lived in Long'an.

Lin Qiupu said, "Captain, isn't He Jingjing He Taiyang's illegitimate daughter? Why is there another father?"

"It may be that her mother had married Li Qiang. In this case, Li Qiang is her adoptive father. There is another possibility that it’s Li Qiang who is the biological father..."

"He Taiyang is the foster father?"

"He should be called godfather. When He Jingjing came to find him, she was already an adult."

"Why did He Taiyang adopt her?"

"What do you think?"

"Mm, I can't think of a reason."

"He Jingjing wasn’t living in He Taiyang's house as a daughter at all, but as a mistress. This isn’t a glorious thing, so he said that she was his illegitimate daughter. I suspect that Madam He discovered this long ago. After all, it’s hard to keep secrets between husband and wife. Therefore, she had a very poor relationship with He Jingjing. He Jingjing and He Taiyang have an age gap of over 30 years, and it was most likely not true love. Based on He Jun’s reaction, he doesn’t know He Jingjing is He Taiyang’s mistress. When He Taiyang got angry with He Jun because He Jingjing and the youthful, strong He Jun had gotten together, he thought he was just a father who didn’t want his daughter to be with someone who had been in jail."

Lin Qiupu admired that Song Lang could make so many inferences at once.

"Of course, these are just my speculations, and we still need evidence to support it... Little Lin, I will set up tomorrow's task for you. You go and look for He Jingjing alone, and have a casual chat with her. The important point is for you to invite her out for a drink. Then you need to take back the cup she drank from and send it to Captain Peng within two hours."

"Collect her DNA? Captain, can't we directly request the person involved in the case to provide their biological data?"

"I don't want to alert her for the time being. Asking someone for their DNA is equivalent to telling them that the police are suspicious of them. If He Jingjing isn’t related to He Taiyang, then she at least has a motive for the murder."

"Motivation for murder?" Lin Qiupu scratched his cheek. The captain's thinking was too fast, and he couldn't keep up.

"Don't think about it. You should go home early to rest."

"Okay, Captain." Lin Qiupu was about to leave when he remembered something. He took out a handful of change from his pocket. "This is the money I got back after taking the taxi just now."

"Save it and buy yourself some snacks!"

"No, even if you’re the captain, I don't want to owe you anything." Lin Qiupu said seriously, handing over the change and the invoice for the taxi to Song Lang before saying goodbye. Song Lang looked at the boy's back and smiled slightly.

Looking at the money in his hand, Song Lang suddenly thought of something and hurried to find Peng Sijue.

"Old Peng, do you have a million in savings?" Song Lang asked when he entered the door.

"You want to buy a house?" Peng Sijue was cleaning the test bench.

"I suddenly thought of something. If the deceased took one million that day, how much would it weigh? Let me look at the photos of the scene. All of them."

Song Lang leaned back on his chair with his legs crossed, looking at the pictures of the scene one by one. It was already 11:00 at night. Besides a few police officers on duty in the bureau, only the two of them were left. Song Lang enjoyed this kind of quiet atmosphere, it was as if the whole world was asleep. It was only in this tranquil atmosphere that his brain could operate at full speed.

"1.15 grams!" Peng Sijue brought over a cup of coffee, "I weighed it with an electronic scale. A hundred-dollar bill is 1.15 grams. If it is an old bill, it might be a little lighter."

"Ten thousand yuan is 115 grams, one million is ten kilograms, which is the weight of a bag of rice."

"That’s the weight of the entire head of an adult male."

"You sure are a forensic doctor. Even the examples you give are so weird." Song Lang smiled. "I’ll go find a ten-kilogram object."

"It should be over ten kilograms. Don't forget the weight of the box!"

The two went to the evidence room. The police evidence room was a treasure house. They had everything. They found a box with ten kilograms of paper in it. Song Lang handcuffed his wrist to the box. "Let’s go for a walk."

"It looks like it's going to rain. Just experiment here."

"No, there’s no atmosphere here. Only the black night and high wind outside provides the right atmosphere. I’ll treat you to supper when I’m done."

Peng Sijue sighed and had no choice but to accompany him.

The weight of ten kilograms didn't feel like much at first. Only after Song Lang did a round of walking, did he discover that it was very heavy. His wrist was handcuffed to the box, so he couldn't change hands. His hand was a little sore from carrying it.

It was about half a kilometer from the Taiyang pawn shop to the scene of the crime. After walking this estimated distance, Song Lang put down the box and breathed a sigh of relief. Peng Sijue said, "You’re really dedicated to your work. Even your wrist is chafed red."

Song Lang looked at his wrist. "I have a professional question. Would blood run out of the mouth with the position where the knife had stabbed the deceased?"

"The deceased's trachea did have some reverse blood flow, and there was some in his oral cavity."

"But there was no blood on the ground. Something was blocking the blood."

Peng Sijue glanced at the box. "The box?"

"Yes, the bending action made by the deceased was actually to put down the box. Why did he put the box down in front of the other person? It’s because the other person was the party who came for the transaction. From this point, it seems that we had misjudged things. The murderer is not necessarily an acquaintance, he was the other party in the deceased’s transaction. When the deceased bent over and opened the box, the murderer drew out the knife and stabbed the deceased in the back. The blood that the deceased vomited was vomited onto the box, and then the murderer took the box with them."

"The ground was very muddy. There would be traces if he put the box down."

"The deceased crawled over that part of the ground and wiped out the indentation. Of course, if you look closely, there’s actually a slight indentation." Song Lang took out a photo of the scene, and a small square indentation could be seen on it.

After seeing this, Peng Sijue was convinced. "This means that you have more subjects to investigate?"

"This is a good thing. The identity of the murderer has become clearer. As long as we find out who the deceased went to see that night, we won’t be far from the truth... But what was this million for... Life-preservation money? It’s definitely not life-preservation money... Could it be money to pay off the old man? Wrong as well... Why did He Jingjing bring out that legend? Does she have other intentions..."

Song Lang pondered and walked away alone with his hands behind his back. Peng Sijue said, "Hey, take the box back!"

Song Lang was completely immersed in his own deductions and turned a deaf ear to Peng Sijue's words. As he walked further and further away, Peng Sijue sighed helplessly, and could only bring the box back to the Public Security Bureau by himself.

Peng Sijue returned to his lab, made a pot of coffee, turned on the music, picked up a book and began reading it. Light rain fell outside the window and Song Lang suddenly ran back. His windbreaker and hair were all wet. He said, "Fuck, I actually walked into a park. You haven't gone home yet?"

"I was waiting for you. Didn't you say we were having supper together?"

"Sorry, sorry, I was too focused on the questions in my head..." Song Lang picked up the coffee on the table and drank it. "It's really bitter. There’s no sugar."

"Sugar can make people tired and cause tooth decay. I never eat sugar."

"See how restrictive your life is?" Song Lang took out a cigarette for himself.

"A self-disciplined life will give you a lot of benefits." Peng Sijue reached out and grabbed the cigarette in his hand and threw it out of the window. "Don't smoke in the laboratory!"