The Mystery of the Inner Demon

Chapter 173 Underground Hole
"Dongji Town is a peninsula formed by land reclamation. Mr. Cui anticipated at the beginning of the design that the concrete caisson structure left after land reclamation would be connected to the sea cave, which would develop a sea erosion fissure zone..." Song Tao explained while placing his fingertips on the place where the contour lines closed.

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

"To be more precise, it's a man-made-natural composite underground space. However, this space is not fixed; it changes with natural subsidence, construction on the ground, or destruction."

Qi Fei's heart sank when he heard this. "According to what you said, the situation now is very different from forty years ago. Even if this void exists, we may not be able to find it now, right?"

Song Tao didn't answer immediately. Instead, he slowly turned on a large display screen beside the conference table. A moment later, a three-dimensional animated model appeared on it. "Thankfully, Dongji Town is a successful case study of land reclamation. We collect data from it every year and import it into this model. Using this model, we can reverse engineer and simulate the underground structure of Dongji Town in 1983."

After saying that, he began to compare the old drawings he found and entered a series of data into the computer. With the tap of the Enter key, the model on the screen began to change. The contour lines and rock masses marked with various colors seemed to have entered a time tunnel, constantly adjusting their shapes and positions.

Under the expectant gazes of the three people, the image finally froze. Song Tao used the mouse to move the position of the three-dimensional image, and finally, not far from the coast, an arched hole appeared in their sight.

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

"Officer Qi, I think this is the first crime scene you're looking for," Song Tao said, moving the mouse across the screen. "This is a typical complex underground space." The cursor moved over a winding curve connecting the cavity. "Look, there's a passage about two meters high that connects to the coast. This indicates that this is an underground space formed by the gradual erosion of the gaps between the concrete caissons by the sea."

Qi Fei studied the image carefully. His recent day-and-night study of Dongji Town's topography had given him a preliminary understanding of these specialized images. He pointed to the line off the coast and asked, "Is this sea level? Does this image mean that the cave entrance is below sea level?"

"That's right, but it's not fixed. The sea level will change greatly due to the tides. This sea level only shows its average level for that year."

The word "tide" stimulated Qi Fei's nerves like an electric shock. He suddenly understood how Ye Ming found out the exact time of each person's death: "The changes in the tide have a fixed cycle, right?"

Song Tao smiled. "Officer Qi, it seems you're very dedicated to your studies. Of course, the tidal cycle is related to the lunar cycle, or to be more precise, the lunar month, which is approximately 29.5 days long."

"Thirty days..." Qi Fei muttered. In his mind, the scraps of paper Ye Ming had left in the aluminum lunch box suddenly took on a different meaning. "The murderer is so stubborn in insisting on a thirty-day killing cycle because his killing altar only appears once every thirty days!"

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

"As for this question, I think that humans conquer their environment, but they are also tamed by nature. The altar in his heart was solidified by the coastal tides of Dongji Town and became part of his own doctrine," Qi Fei said. "Ha, Brother Fei, the way you say that really sounds like Zhong Kui," Wu Shanqiu laughed.

"If the murderer committed the crime in this underground cave, many things can be explained..." Qi Fei was immersed in the excitement of getting closer to the truth. "Before, we couldn't understand why there were 80-year-old pine sawdust in Lin Suzhen's fingernails, and why abnormal levels of deep-sea diatoms were detected in the mud on her soles..."

Song Tao immediately realized what was going on: "Officer Qi, the Lin Suzhen you mentioned is also a victim, right? The two things you mentioned are very likely to appear in this underground cavity. Pine piles are our common support materials. As for deep-sea diatoms, it is very common for them to remain in the mud in this cavity when the tide rises."

Song Tao's words made Qi Fei more confident in the direction of his investigation, and he hurriedly said: "Teacher Song, can this model infer whether this space still exists now?" His fists clenched unconsciously. If this place had not been buried, it meant that more than 40 years later, the physical evidence at the first crime scene was likely to be preserved intact. He didn't dare to think about what this meant.

"Let me try." Song Tao said, and input another string of instructions, and the model began to continue changing.

When the image froze again, Song Tao used the cursor to demonstrate the area. "The good news is that, theoretically, the underground cavity is still there. The bad news is that a section in the middle of the tunnel has collapsed. Entering this underground cavity requires professional exploration personnel and equipment. Of course, if you need it, we can provide assistance."

Song Tao uttered a puzzled sound as he spoke. "One thing is quite strange. The rock mass in the middle section of the collapsed tunnel exhibits a discontinuous shear surface, indicating a sudden brittle fracture. It's likely not caused by natural subsidence."

Following Song Tao's instructions, Qi Fei carefully looked at the location where the passage collapsed. Suddenly, he thought of something and hurriedly said, "Teacher Song, can you adjust the perspective to a bird's-eye view?"

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

The channel is in a flat U-shape. Although the entrance is near the coast, the middle section is below the town.

Qi Fei had devoted himself to the investigation during this period, so he could see the map of Dongji Town with his eyes closed, and the location of the collapse was either somewhere else or the location of the new aquatic products building.

Qi Fei took a deep breath and said, "It seems that our guess was wrong. The report in the 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 in confusion, "Brother Fei, what did you say?"

Qi Fei pointed to the point on the map and said to Wu Shanqiu, "We've always wanted to know why the murderer suddenly changed the location of the murder from Dongji Town to the urban area of ​​Nancheng. This is the reason!"