Chapter 173: Underground Cavity

"Dongji Zhen belongs to the peninsula landform formed by land reclamation. Old Cui predicted at the beginning of the design that the concrete caisson structure left after land reclamation would connect with the sea erosion cave, which would develop a sea erosion fissure zone..." Song Tao explained while letting his fingertips fall on the place where the contour lines closed.

"That is to say, there is a cavity underground, right?" Qi Fei asked immediately.

"To be precise, it is an artificial-natural composite underground space. However, this kind of space is not fixed. It will change with natural settlement, construction on the ground, or destruction."

Qi Fei heard this, and his heart sank: "According to your statement, the situation now is very different from more than forty years ago. Even if this cavity exists, we may not be able to find it now, right?"

Song Tao didn't answer immediately, and unhurriedly opened a huge display screen beside the conference table. After a while, a three-dimensional dynamic model appeared on it: "Fortunately, as a successful case of land reclamation, we collect its data every year and import it into this model. Through this model, we can simulate the underground structure of Dongji Zhen in 1983 by reverse deduction."

After finishing speaking, he began to compare the old drawings he found and input a series of data into the computer. With the pressing of the Enter key, the model on the screen began to change. Those contour lines and rock bodies marked with various colors seemed to enter a time tunnel, constantly adjusting their shape and position.

In the expectant eyes of the three people, the image finally froze. Song Tao moved the position of the three-dimensional image with the mouse, and finally, not far from the coast, an arched cavity appeared in their line of sight.

"Ah, could this be..." Qi Fei only felt that his throat was suddenly dry, and his tone of voice became distorted with excitement.

"Police Officer Qi, I think this is the first crime scene you are looking for," Song Tao said, moving the mouse on the screen, "This is a typical composite underground space." The cursor wandered on a winding curve connecting the cavity, "Look, there is a passage about 2 meters high here, which connects to the outside of the coast, indicating that this is an underground space formed by the gradual erosion of the concrete caisson gap by seawater."

Qi Fei looked at this image carefully. The recent day and night study of Dongji Zhen's terrain gave him a preliminary concept of these professional images. His finger pointed to the lines outside the coast: "Is this sea level? Does this picture mean that this cave entrance is below sea level?"

"That's right, but this is not fixed either. Affected by the tides, the sea level will change greatly. This sea level mark is its average level back then."

The two words "tides" stimulated Qi Fei's nerves like an electric shock. He suddenly understood how Ye Ming found the exact time of each person's victimization: "The change of tides has a fixed cycle, right?"

Song Tao smiled: "Police Officer Qi, it seems you are studying very hard. Of course, the tidal change cycle is related to the lunar phase cycle. To be precise, it is a lunar month of about 29.5 days."

"Thirty days..." Qi Fei muttered. The paper slips Ye Ming left in the aluminum lunchbox suddenly had a different meaning, "The killer is so stubborn in insisting on a thirty-day murder cycle because his murder altar can only appear once every thirty days!"

"But Brother Fei, if this is the reason, then those victims including Ye Ming were killed in Nancheng urban area. Why does this cycle still exist?" Wu Shanqiu raised an objection.

"This question, I think, humans will conquer the environment, and they will also be tamed by nature. The altar in his heart was solidified by the tides of the Dongji Zhen coast, becoming a part of his self-created doctrine," Qi Fei said.

"Ha, Brother Fei, the way you say this is really like Zhong Kui," Wu Shanqiu laughed.

"If the killer committed the crime in this underground cavity, many things can be explained..." Qi Fei was immersed in the excitement of approaching the truth, "Before, we couldn't figure out why there would be 80-year-old pine wood chips in Lin Suzhen's fingernails, and abnormal content of deep-sea diatoms would be detected in the silt on her shoe soles..."

Song Tao heard this and immediately realized: "Police Officer Qi, you said Lin Suzhen is also a victim, right? These two things you mentioned are very likely to appear in this kind of underground cavity. Pine wood piles are common support materials we use. As for deep-sea diatoms, it is very common for them to remain in the silt of this kind of cavity when the tide rises."

Song Tao's words made Qi Fei more confident in his investigation direction, and he hurriedly said: "Teacher Song, can this model infer whether this space still exists now?" His fist clenched involuntarily. If it was not buried here, it means that after more than forty years, the physical evidence of this first crime scene is likely to be well preserved. He didn't dare to think what this meant.

"I'll try," Song Tao said, and input a string of instructions, and the model began to continue to change.

When the picture froze again, Song Tao demonstrated in that area with the cursor: "A good news, theoretically, this underground cavity still exists. The bad news is that a section in the middle of the passage has collapsed. If you want to enter this underground cavity, you need professional exploration personnel and equipment. Of course, if you need it, we can provide help."

Song Tao said, and made a puzzled sound himself: "One point is quite strange. The rock body in the middle of the collapsed passage shows a non-continuous shear surface, indicating that it has undergone a sudden brittle fracture, which is likely not caused by natural settlement."

Following what Song Tao pointed out, Qi Fei looked carefully at the location of the passage collapse, suddenly thought of something, and hurriedly said: "Teacher Song, can you adjust the perspective to overlook?"

As the model rotated, the location of the collapse clearly appeared on the map of Dongji Zhen.

This passage is in a flat U-shape. Although the entrance is near the coast, the middle part is under the town.

The wholehearted investigation during this period of time allowed Qi Fei to see the map of Dongji Zhen even when he closed his eyes, and this location of the collapse is not other places, but where the new aquatic products building is located.

Qi Fei took a deep breath: "It seems that our speculation direction is wrong. The report of Nancheng Daily that Ye Ming circled has nothing to do with the construction company!"

Wu Shanqiu looked at Qi Fei's sudden realization and asked puzzledly: "Brother Fei, what did you say?"

Qi Fei pointed to the points on the map and said to Wu Shanqiu: "We have always wanted to know why the killer suddenly changed the place of murder from Dongji Zhen to Nancheng urban area. This is the reason!" ===== CHAPTER 174 =====