Chapter 936: The Next Few Days

The next few days were spent in the dull routine of investigating the case.

Each team conducted investigations according to their established goals. Liu Jinghui redid the timelines for several key personnel, while Jiang Yuan began receiving an increasing number of reports on trace evidence, which he read with great interest.

Using trace evidence to investigate a case is a luxury; ordinary criminal investigation teams only use it on key evidence for major cases. It's not that they can't afford the 500 yuan, but that DNA is more cost-effective.

Unlike DNA, even if the results of trace evidence are obtained, it can only be said that a certain substance existed at a certain place and time; there are still quite a few steps remaining before the case can be solved.

By contrast, if someone's DNA is found at a crime scene, there must be an explanation for it.

"How's it going?" Liu Jinghui, tired from writing and drawing, sat down next to Jiang Yuan and casually grabbed a box of Zhonghua cigarettes from the table.

Jiang Yuan smiled at the sight, turned to take out a cigar humidor, opened it, offered one to Liu Jinghui, took one for himself, and said while clipping it: "A lot of results from the trace evidence have come out, but specifically speaking, they might still need some analysis."

"Cigars... this will take an hour to smoke, right?" Liu Jinghui didn't follow up on the previous topic; he also lowered his head to clip his cigar, thinking as he did so.

"Just about. It's a good time to rest and clear our heads," Jiang Yuan said.

"I don't really know how to smoke them; it'd be a waste."

"Same here. My old man bought them, I'm just playing around with them, no waste involved. They're just Cuban agricultural products. My old man first got them when he was buying cattle; the merchant selling the breeding bulls gave them as a gift." Jiang Yuan chatted idly as he lit the cigar.

Cigar smoke is ten times denser than cigarette smoke, and since it's smoked continuously, even if the exhaust fan is spinning at full speed, it only takes a short time for a meeting room to become shrouded in mist, looking like a celestial realm.

Jiang Yuan and Liu Jinghui smoked for a while, achieving the effect of 20 criminal investigators holding a meeting together. At that moment, the two in the meeting room looked at each other and suddenly felt the urge to discuss things.

Generally speaking, when a meeting reaches this point, it's like being slightly tipsy from drinking—it's time to start talking about business; otherwise, dragging it out any longer would be bad for everyone's health.

"Do you want me to help you analyze it?" Liu Jinghui took a puff of his cigar, let the smoke swirl in his mouth twice, and then exhaled. As for not knowing how to smoke cigars, that was naturally just something he said casually; if a provincial bureau expert didn't even know how to smoke a cigar, how could they help the tobacco department crack down on crime?

"Let's look at it together." Jiang Yuan pushed the boxes of reports in front of him forward.

A single trace analysis report is just two thin sheets of paper, but when hundreds of them are stacked together, it's quite a lot. It's a bit like the homework gathered from poor students—you know most of it is useless, but you still have to force yourself to read through it, spending time searching for something potentially useful among a pile of useless content.

"You took samples from many points on the windows and door locks?" Liu Jinghui didn't understand "reading" analysis reports in the scientific sense, but he had his own way of reading—which was reading Jiang Yuan.

Jiang Yuan took a sip of tea, said "Hmm," and replied: "The indoor environment is quite complex, and these are all leftover evidence, mainly clothing, bed sheets, and objects. I didn't see anything from the samples I took. As for the windows and door locks... the killer must have had an entry point, right?"

"What if the suspect was let in, or tricked them into opening the door?" Liu Jinghui reminded him.

"If they were tricked into opening the door, they wouldn't have hidden the son." Jiang Yuan had naturally thought of that too.

"That reasoning makes a lot of sense." Liu Jinghui was pleased, then became a bit more serious: "However, if it was the daughter who opened the door, and then a conflict occurred with the person entering, and the mother hid the son before going out to help the daughter, only for both to be forced into the bedroom and killed—wouldn't that hypothesis better explain why the son was hidden but the daughter wasn't?"

The smoke in the meeting room became even thicker.

Liu Jinghui had long had this suspicion, which is why he had ordered a reinvestigation of the daughter's social circle. It was only because there were no conclusions that he hadn't brought this line of investigation back up. Now that Jiang Yuan had proposed it, Liu Jinghui naturally had to add this possibility.

Jiang Yuan nodded slowly as he listened; as for conjectures, as long as there's a possibility, that's enough.

"Of course. There are many other reasons why the son was hidden and the daughter wasn't." Liu Jinghui added: "It could also be that the daughter was too big. There are only two places in the bedroom easy to hide someone: the wardrobe and under the bed. An 8-year-old boy can be hidden in the wardrobe if you pile clothes up, but given the daughter's height and build, even if you wanted to hide her, she could basically only be hidden under the bed. And there's nothing to block the view under the bed, so it's possible the daughter was hidden but discovered and dragged out."

Liu Jinghui's reasoning was very clear and had a good sense of direction. Jiang Yuan couldn't help but nod; such a possibility certainly existed.

"I get quite excited when I talk about these things." Liu Jinghui realized the topic had drifted, laughed, turned his head, and said: "You mentioned the entry point earlier, which immediately made me think of the locked-room murder aspect. Hmm, what did you find on the door locks and windows?"

"Nickel, copper, chromium, carbon, iron..." Jiang Yuan showed Liu Jinghui the conclusions of the trace evidence from the points taken on the door lock.

"What does that indicate?"

"How should I put it?" Jiang Yuan hesitated for a moment and said: "From the perspective of trace evidence, this conclusion actually cannot provide a decisive result. But from the perspective of investigative analysis... although the appearance of these metal elements is normal, the fact that so many elements were found in the first set of samples..."

Jiang Yuan simply pulled over a whiteboard, drew the shape of a keyhole on it, pointed to a few spots, and said: "We dismantled the lock because, in my view, there were too many scratches inside the keyhole, exceeding the level of a normal lock. Of course, this judgment is based on experience... Next, we took samples from a wide range of points, and we could see that the range of various metal elements appearing inside the lock was beyond the normal scope."

If a young technician had said this, it certainly would have been hard to convince anyone, but when Jiang Yuan said it, Liu Jinghui immediately followed his line of thinking.

"You mean—let me understand first... these metal elements you mentioned were brought by the key and don't belong to the lock itself?" Liu Jinghui grasped the point immediately.

Jiang Yuan nodded: "Elements like chromium and nickel, at the very least, are not from the lock itself. However, there are no typical signs of technical lock-picking inside this lock. So, it can be understood as being brought by a key."

"But beyond the scope? Beyond the scope of a normal key?"

"Beyond the scope of the key for that lock." Jiang Yuan patted his forehead as he said this: "Was it a newly cut key? That doesn't seem right either; a newly cut key wouldn't leave so many marks..."

"Wait, let me understand again!" Liu Jinghui was very interested in any new clue, thinking as he spoke: "Could it be said that the newly cut key was actually larger than the original, so it poked deeper and left deeper marks?"

"Hmm... although it's not entirely like that, we can add one more point: a newly cut key is also rougher. Even though the person cutting the key would polish it, the grooves and ridges on the key are very fine. Even with careful polishing, they can't be completely smoothed out, so it would take several pokes before it fits relatively well..."

"So someone used a newly cut key to open this door?" Liu Jinghui slapped his thigh, feeling a sudden sense of clarity.

Jiang Yuan had to pour cold water on him: "It's not that simple. If it were just opening the door once, it shouldn't leave so many extensive marks. If it were a newly cut key, it might have taken a dozen or even twenty pokes to leave so many fine marks, especially the protrusion marks. So, it feels more like a new type of lock-picking tool..."

Jiang Yuan stopped there.

Liu Jinghui urged him: "A new lock-picking tool? Doesn't that make the target even clearer?"

"Yeah, I've been doing research in this area for the past few days. If there's a new lock-picking tool, I think the killer wouldn't be able to resist using it. It's impossible to use it only once and then give up." Jiang Yuan looked at Liu Jinghui as he spoke, deciding to be more rigorous: "Of course, we can't rule out that the killer is just that cautious, but if that's the case, it would be very difficult to find the killer through the lock-picking tool..."

"Have any new lock-picking tools been released in the last few years?" Liu Jinghui asked suddenly.

"Lock development has been very slow... Hmm, we could also follow your line of thinking to investigate. The killer might not dare to sell the lock-picking tool they once used, or continue using it, but they might make a living from it, specialize in researching this kind of thing, or open a company?" Jiang Yuan wasn't very certain. This condition sounded simple but was actually very broad. Theoretically, everyone in lock companies, people in the lock-picking business, safe-cracking business, and the trendy electronic lock industry could be within the scope. This list would either be too large or miss someone, the kind that even Xu Taining couldn't screen.

Liu Jinghui puffed on his cigar, continuously exhaling thick fog.

He realized the low practicality of Jiang Yuan's plan better than Jiang Yuan did. Perhaps they could operate in reverse: first determine the list of suspects, then see if they have any work direction related to locks, or have suspicions and reputations regarding theft and burglary...

But in reality, even without Jiang Yuan's deduction, if a suspect had experience in this area, they would be specially noted anyway.

And if they wanted to investigate forward, connecting the killer to the locks and then searching for the killer, it would still be very difficult. Because making locks, or developing a new type of lock, isn't really a lucrative trade, and being a burglar is obviously not an indispensable lifelong career.

Theoretically, if the killer really had talent in this area, they could have made a special, new type of lock-picking tool 10 years ago that even Jiang Yuan couldn't identify. Then, 10 years later today, they might have already made a name for themselves in mechanics or something else, and wouldn't need to show off this kind of talent at all.

If the killer was a peer of the daughter from 10 years ago, calculating the time, the killer would have just graduated from university, and might have even gone to a good school for a master's degree, and used their good brain to study a completely different major.

Perhaps this is the truth...

Liu Jinghui thought of this, shook his head vigorously, put down the cigar, and said: "We can't consider it from this direction."

"Hmm?" Jiang Yuan was puzzled.

Liu Jinghui: "I mean, weren't we just talking about a newly cut key? Compared to inventing a brand-new lock-picking tool that you don't even know about, isn't the fact that a key was newly cut more reasonable? Occam's Razor: if a simple explanation works, don't use the complex one."

"A newly cut key cannot explain the large number of fine scratches." Jiang Yuan had been turning this thought over for several days too.

"Indeed." Liu Jinghui picked up the cigar again and puffed on it for a while: "Actually, no matter which conjecture it is, if we assume the door lock was opened abnormally, it can be understood as a crime not committed by an acquaintance. This also explains the situation where the surviving little boy said there were two killers. It is quite common for burglary or robbery to be committed by multiple people... Hmm..."

Jiang Yuan listened to the sound and looked at Liu Jinghui: "What did you think of?"

"Burglary or robbery committed by multiple people, although not necessarily a fixed gang, are usually experienced hands. Especially those capable of technical lock-picking, it's impossible for them to stop after doing just one such case. Even if they killed someone, it's impossible that they just happened to use a new invention for their first crime and then gave it up? Thieves don't have that kind of self-control." Liu Jinghui shook his head. Being a thief is an addictive profession; once many people enter this profession, they won't easily give it up. It's an evergreen tree in the criminal system.

Liu Jinghui thought, smiled apologetically at Jiang Yuan, and said: "I think the idea of technical lock-picking can be put aside for a moment."

"Okay." Jiang Yuan agreed readily.

"Speaking of which, I have an idea." Liu Jinghui simply pulled over a whiteboard and said: "If the killer cut a key... I know, you just said that the scratches produced by a newly cut key couldn't be that numerous, but is it possible that the killer cut many keys... no, it should be that they cut the key many times? Poke once, can't open it, then poke again or cut the key again, and then try?"

Jiang Yuan's eyes lit up: "Let me see."

As he said this, Jiang Yuan immediately went to get the dismantled lock and looked closely at the lock cylinder under the horseshoe mirror.

The magnification of the horseshoe mirror wasn't high, which made Jiang Yuan frown, and he shouted: "Open the windows, open them all, let the smoke out."

The smoke from the cigar was thick, and at least to Jiang Yuan's perception, it was affecting his observation.

The windows of the meeting room had actually been wide open for a long time, and the exhaust fan was working as hard as it could. Liu Jinghui shouted for people to come in, each holding a fan or useless documents to fan the air vigorously, and threw both cigars out the door.

Once the smoke cleared, Jiang Yuan looked up: "Very possible, very possible! A very good conjecture."

"Can this be proven?" Liu Jinghui was just guessing; he never thought this could be proven technically. He usually relied on catching people and interrogating them.

Jiang Yuan nodded vigorously: "The scratches inside the keyhole show a repeated cycle of scratching and polishing; scratching and polishing, then scratching and polishing again, which is why it looks so strange. If someone used a newly cut key to open the door, regardless of whether they opened it or not, there would be heavy scratches inside the keyhole. But the subsequent process of continuously trying to open the lock is equivalent to polishing away a part of these scratches..."

Jiang Yuan: "The size of the key cut by the killer was inconsistent; some might have been a bit longer or larger than the original, which would create deeper scratches. The marks inside the lock cylinder don't fit the marks of a newly cut key opening the lock once, and they don't even quite fit the marks of opening the lock a few times, but they do fit the marks of opening the lock many times, irregularly. This is a bit like the tentative wounds in forensic medicine, indicating that the criminal had many tentative attempts before committing the crime. The time for these tentative attempts could have lasted for one or two months, or two or three months."

Liu Jinghui became excited as he listened: "If that's the case, the killer wouldn't be a pure stranger. The victim's family didn't have much money, and no valuables were lost. If the killer was a stranger, there would be no need to keep staring at their house. In this way, it's very likely that the killer came into contact with the victim's key through some means, then cut one themselves, and then kept trying?"

"Very likely." Jiang Yuan looked at the horseshoe mirror again and nodded continuously: "It's very likely they cut a key first, couldn't open it, then took it back to file it with a file, then came back to try again, still couldn't open it, then went back to file it again. This better explains the change in the key's size; the file made the key a bit smaller and reduced the roughness, but the length basically remained the same!"

"An acquaintance... or someone not that close, but who could come into contact with the key." Liu Jinghui nodded continuously: "I'll make a list!"