"Then what?" Chen Shi asked.

"I said that doing this was risky, and that we needed to buy some equipment. I gave him some money and the first price that came out of his mouth was a million. I told that kid he was crazy. I gave him 400,000. No more, no less. Just the 400,000. I transferred the money over to him on the spot.”

"Why 400,000? Does this number have any special meaning behind it?"

Director Wei was silent for a moment. "Old Geng borrowed 400,000 yuan from me before. Both of us knew what 'borrowing' meant. It meant giving it to him for nothing! He said that he wouldn’t send out the letter if I gave him 400,000 yuan. I was going to give him the money when I went over to his house that day, but what he said sounded so awful. He acted all high and mighty even when he got a bargain. He was just so petty. So I changed my mind..."

"You thought that instead of giving him money, you might as well use the 400,000 to hire a killer to get rid of him?"

Director Wei nodded his head heavily and looked as if he had accepted his fate. "Back when I was active in the underworld, I got to know a few ruthless characters, but when I contacted them, I found out that they had either turned over a new leaf or had been executed by the Public Security Bureau. None of them were useful. While I was venting, my brother-in-law said he could handle this matter, so I gave him the money. I told Hua Chao that he had to keep the matter a secret no matter what once the money was given to him. Even if the police held a gun to his head, he mustn’t sell me out. I didn’t know he was so weak, haii!”

"After that?"

"I was very happy to hear that Old Geng was dead. It seems that this kid had done it. We haven't been in contact for a while, just to prevent suspicion from the police. I didn't know you guys would be so tricky and even check my bank account."

At the end of the interrogation, Lin Dongxue asked, "The case counts as solved, right?"

"No, Hua Chao didn’t confess to the murder. Director Wei thought he did it. In fact, this kid isn’t so capable."

"It's a capital offense if he confessed. He definitely wouldn’t do that. Do you want to try interrogating him again?"

"You interrogate him. I'll check the surveillance footage."

Lin Dongxue felt that they were one step off from getting the confession, but no matter how she asked, Hua Chao refused to admit to murder. In fact, he didn't know the details of Geng Zhangle's death. He said that he had planned to find a brother from the underworld and give him 200,000 yuan to get rid of the old man. That way, he could make money without taking any risks.

"What's the name of that brother of yours?"

"Wang Yiming."

Unexpectedly, this person actually existed and when he was brought back for interrogation, he was just as scared as Hua Chao. He admitted that he had received Hua Chao’s money, but he denied the murder. He said that he had been pondering things over at home for a long time. Rumor had it that there was a powerful person in the second team of the criminal police that solved any case that came by, but he wanted to make money, so there was a fierce internal struggle in his heart.

Finally, Wang Yiming scouted for and found a new gang recruit, gave him 100,000 and asked him to push the old man onto the road and get him run over by a car while he was out. That way, he wouldn’t be taking any risks and could make money.[1]

"What's that youngster’s name?" Lin Dongxue was already quite tired by this stage of the interrogation.

"Xi Xiaohu."

Later, Xi Xiaohu was summoned for an interrogation. He was still a minor and was dressed in a very non-mainstream manner. It was the first time he was facing the police in the interrogation room, and Xi Xiaohu was so scared that he almost pissed himself. He admitted that he had received Wang Yiming’s money. He was very happy at the time about earning 100,000, but he was afraid of killing someone and going to jail, causing his parents grief. After lots of thought, Xi Xiaohu thought of a brilliant idea...

"Hire someone else to be the killer?" Lin Dongxue had already guessed his lines.

"Wow, Police Elder Sister, you are so smart. You guessed it on your first try. I found a person on the Internet. They claimed to be a retired Vietnamese special forces soldier who had killed dozens of people. I could pay 20,000 yuan as a deposit first, and then pay the 30,000 yuan balance after the mission was accomplished. I thought that in this manner, I could make money without taking any risks.”

"And then?"

"Motherfucker, I got scammed!"

Lin Dongxue wondered whether these hooligans were reliable or not. After checking their cash flows, Hua Chao had indeed received 400,000 from Director Wei, Wang Yiming had received 200,000 from Hua Chao, and Xi Xiaohu had received 100,000 from Wang Yiming and then transferred 20,000 yuan to an online account.

Everything fitted together nicely. It seemed that none of these people had actually committed the crime.

Chen Shi carefully watched the surveillance footage at the park. Hua Chao didn’t show up on that day, so the group of people were all released.

After conducting interrogations all morning, Lin Dongxue was very tired and said disappointedly, "The lead is a dead end."

"Don't be impatient. I found someone on the surveillance footage. Guess who it was."

"Don't act mysterious. I don't have the strength to guess right now."

"Geng Qing's boyfriend."

"Really?"

Chen Shi shrugged, "The body stature and hairstyle are a bit similar. The footage is too blurry, and I can't see his face clearly."

"But what motive would he have for murder?"

"I said before that a murderer's motive must be hidden, so let's dig deeper!"

They needed a reason to visit Geng Qing. Fortunately, they needed to send Geng Zhangle's body back. Chen Shi went to look for Peng Sijue. Peng Sijue sat in the laboratory with a courier box in front of him, facing a cylindrical object in a daze.

"Old Peng..."

"Come here!"

Chen Shi walked over. Peng Sijue grabbed his arm and poked it with the cylinder. Chen Shi felt as though he had been flicked by a finger. He drew his hand back and saw a round red dot on his arm.

"What is this?!"

"I’m doing an experiment, and what I injected just now was saline."

"This is a syringe?"

"Yes, a needleless syringe. This type of syringe uses pressure to squeeze the liquid drug into the capillaries. In fact, it has been available since the 1990s. The disadvantage is that the dosage is too small and the production cost is high. It’s currently being used by patients to inject themselves with insulin."

Chen Shi looked at his arm and said, "It’s exactly the same as the mark on the corpse."

"Captain Peng, I have a suggestion that’s a bit amateur." Lin Dongxue said, "Could the murderer not have injected anything at all, and just injected air into the blood vessels? It’s said that air embolisms are not easy to detect."

"This possibility has been ruled out. We used the diluted blood serum of the deceased in animal experiments to prove that it was indeed a toxic substance."

"Oh... By the way, I saw a very ingenious method of killing when I was watching a TV series. The formalin you use is poisonous. One of the murderers used formalin to kill someone, and then the body was immersed in formalin. Forensic pathologists couldn’t detect it either.

"Formalin is not used for autopsies. That kind of thing is very pungent. If you really use it to kill people, it’s impossible not to detect it. Unless you kill someone and donate it to a medical university as a ‘silent teacher’[2] after soaking for a long time."

Lin Dongxue smiled awkwardly, "These are just the opinions of someone outside the field. I wanted to see if I could help you."

"These opinions are very good, and laymen can sometimes see things that experts can't see." Peng Sijue said with a smile.

"Then let a layman like me boldly ask: Why would the murderer mix cocaine in the poison?" Chen Shi asked.

"That's an interfering substance. People who have no history of drug use will experience varying degrees of hyperactivity in the heart, lungs, liver, and kidneys when they are injected with cocaine for the first time. This prevents us from determining the type of toxin through pathological signs."

"It looks like this poison must act on the heart, lungs, liver, and kidneys."

"You layman!" Peng Sijue rolled his eyes at him. "Almost all poisons target one or two of these four organs. Disruptors are very troublesome. I once tested tetrodotoxin, which requires many deproteinization processes in order to find the 'culprit'. If it weren’t for the knowledge that the deceased had died from eating puffer fish, it would have taken a lot of time..." After speaking, Peng Sijue seemed to have had an epiphany. "Protein toxins, why didn’t I think of that... "

He stood up to take a sample for a test. Chen Shi said, "I came looking for you because I wish to take the body away..." Peng Sijue couldn’t even hear him.

1. I believe this was inspired by this real case: https://www.theguardian.com/world/2019/oct/22/the-five-reluctant-hitmen-of-china-group-jailed-over-botched-contract-killing.

2. Donate a body to science for medical students to practise on.