But we know that any crime will leave traces. If there are none, then it's unless this thing is not a physical entity.
However, we police cannot believe in ghosts and spirits. Even if the perpetrator walked barefoot, traces would be found under the wide-spectrum light source, revealing microscopic marks left on the ground by the killer. This is the result of scientific development.
I took out the prepared equipment. It wasn't that I didn't believe the conclusions of the trace examiners and detectives, but I wouldn't feel at ease without personally inspecting it once. However, the result was indeed that nothing was found.
When Liu Yuning came out, I asked her how things were. She said, "It's so strange, it's really like nothing was left. I'm referring to the killer's traces. Although what we see now are just superficial phenomena, the forensic department has already reached this conclusion."
"If I didn't hold onto a sliver of hope, I wouldn't have come back here to look. You don't know how the forensic colleagues' faces drooped when I said we wanted to revisit the scene just now."
"Of course, you want to re-examine, which shows you don't trust their results."
"We really haven't found anything yet, but this is for the best. At least I can be at ease. But the problem remains, Yuning, you should know that even porphyria patients, without sweat glands, would leave footprints, unless this person can fly and commit the crime?"
"No, I actually have an idea. Although this place isn't a locked room, the principle should be similar. I once investigated a drone murder case. The incident happened at a bar, where a client was in a private room dining with a woman. But for some reason, while the woman went to the restroom, the client suddenly died mysteriously.
The police investigated and found no murder weapon. However, tiny needle marks were found on the victim's neck. Later, upon analyzing his heart blood, the victim was found to have been poisoned. A silver needle was discovered on the occipital bone, and the poison was coated on it. Later, when we investigated the woman, she had a conflict with the client, and the woman had also had a child with the client. At the time, we all suspected her of murder due to the motive, but she had a solid alibi.
If we hadn't later discovered that she had worked at a drone company, we wouldn't have thought of a way to solve the case. We then found evidence that after leaving the private room, she remotely controlled a drone from the restroom to infiltrate the room through the window and shoot a poisoned needle, killing the client. Only then were we able to apprehend the perpetrator. Although the drone was the one that killed, the person controlling it was the true murderer. At the time, no traces of her poisoning were found at the scene, and even surveillance footage didn't capture it, which made the initial investigation extremely difficult."
"So, if a drone is used for murder, the killer can leave without a trace after committing the crime? But what about disposing of the body? A dead person can't dispose of themselves, right?" I asked, confused.
"Haha, what are you talking about? Of course, that's impossible. But it's not impossible to use a drone to lift a person, just like our provincial department's former 'Little Doudou.'"
"It seems this killer possesses astonishing drone technology."
"Actually, this is not surprising. Similar locked-room murders have occurred before. In the old era, mechanical hidden weapons were used. Although those devices were not as advanced as drone technology, they could still be used to kill a person. I remember that such mechanical hidden weapon assassinations frequently happened in the island nation."
"Exactly. If that's the case, there should be some traces of the body being lifted and moved at the scene," I said, looking around. I noticed some bloodstains pointing towards the balcony. I was immediately astonished and imagined the scene inside the house. Did the guy lift the person away directly from the balcony?
I had previously wondered why there were no such drag marks in the direction of the door. The investigators at the time probably hadn't considered the possibility of the body being removed through the window. It's easy to imagine that the body was lifted and lowered from the balcony by a drone. If there were any witnesses nearby, they would have been terrified. However, the investigators had canvassed the area, and no one saw anything.
Perhaps the killer precisely targeted a time when everyone was asleep, luckily evading the discovery of witnesses, and then remotely disposed of the body using a drone. If future murderers are this sophisticated, it will be even harder for us to find suspects. However, our technology is also constantly improving.
I don't know if He Xin can find a breakthrough because of our discovery. After taking pictures, Liu Yuning and I returned to the provincial department. After we shared our findings with everyone, no one questioned it. Instead, everyone looked enlightened. He Xin said, "This kind of remote signal is different from a mobile phone call; it leaves no record. Although the killer appeared near the residential area before and after the incident, the waveband disappears once it's used, so I can't trace it. But now, at least we have a new indicator. Let's re-examine Zhang Yangcheng's interpersonal relationships and see if any of his friends work in this field or possess such technology."
"The woman who appeared in his diary before is highly suspicious, but apart from those textual descriptions, we haven't found any trace of her!" Gao Mingqiang said.
"Although it's only text, this person definitely exists. And Dao Zhiyong's comparison confirms that the text is from the deceased without a doubt. The handwriting is identical."
"I know, team leader. I'm not saying the diary is fabricated. Even the killer wouldn't do that, as it would only make themselves more easily exposed. If the killer is indeed the woman from the diary, she must be in hiding now, avoiding exposure to protect herself, unless she had another motive for killing, such as a crime of passion or a targeted murder..."
"Apart from being HIV positive, the deceased also worked in a bar. Other than that, there seems to be nothing unusual about her," Xie Chuchu said.
I also thought about it, but with only one victim, there wasn't enough basis to find a commonality. Everything might just be a coincidence.
Yuan Hezhi remained silent, continuously typing on the keyboard. I knew that he always made discoveries when he was so focused. Indeed, after a minute, he suddenly exclaimed, "As expected! I investigated several drone technology companies in our city. There aren't many, only five. After all, this technology isn't very widespread yet. Of these, only three can produce drones. I checked them all. Three female employees have recently resigned, for unknown reasons. However, their resignations all occurred the day before Zhang Yangcheng's incident. And they all had a common characteristic when they left..."