He then pulled up the on-site photos in the case file and focused on two relatively new weld points on the bottom of the ship: "I noticed that the case file recorded that these two weld points were newly made."

"I suspect that this is what the murderer left behind when they resealed the area after entering and leaving."

One of the team members took a closer look and asked in confusion, "But there are many welding marks on the bottom of the ship. These few look no different from the others."

Ji Shuyun didn't speak, but quickly retrieved high-resolution microscopic photos of all the historical repair welds on the ship and compared them side by side.

“It’s different.” He pointed to the screen. “Look at the welding techniques used on these two new solder joints.”

"The direction of the weld marks, the density of the fish-scale pattern, and the way the arc ends are completely consistent, which clearly indicates that the same person welded them at the same time."

“But look,” Ji Shuyun switched the view to other old solder joints.

“These solder joints left from our early internal repairs are completely different in technique and texture from these two.”

There was a moment of silence in the office, followed by a few low gasps.

"Group Leader Ji...you even understand welding techniques?!"

"My God, to be able to notice such subtle differences... that's an amazing level of observation."

Ji Shuyun's gaze remained fixed on the interwoven metallic patterns, her tone calm yet resolute:

"The murderer's skills and our repairman's habits are very different."

The moment he finished speaking, his father Ji Yanqing's face suddenly appeared in his mind.

That was something his father had casually said many years ago when he was helping him assemble a ship model, while smoothing the seams with a small file.

“When welding underwater, the water flow will push your hands, the mask will block your vision, and even the rhythm of your breathing will affect the welding torch.”

My father used his fingers, which were covered in metal shavings, to touch the simulated weld seam on the model. "So the weld marks are like handwriting, and everyone's handwriting is different."

Ji Shuyun snapped out of her thoughts, met the still surprised looks of her group members, and added:

“These experiences were taught to me by my father. He used to serve in the Marine Corps.”

The Marine Corps has a high-intensity mission and spends most of its time at sea.

After Ji Yanqing and Xia Tang got married, in order to take better care of his wife, he applied to transfer to become a criminal police officer.

Although criminal police officers are just as busy, at least their location is relatively stable, allowing them to provide more protection for their families.

When the group members heard that Ji Shuyun said it was her father's experience, their eyes were full of admiration: "That's amazing! This experience is like a family secret."

Ji Shuyun steered the conversation back on track: "Since they are not a formal ship engineer, they are likely very familiar with another type of 'ship'—illegally modified vessels."

Everyone immediately realized: "That's right! Only seasoned veterans who have been modifying ships in the gray area for years need to master this underwater welding technique, and only they can be so skilled!"

"They risked killing three coast guard officers, and the modus operandi was so swift... This doesn't seem like a spur-of-the-moment decision; it's more like a cover-up by a well-established criminal gang."

Another person added, "Either the Seahorse 173 stumbled upon their secret, or it was targeted as retaliation."

Ji Shuyun nodded, lightly tapping the two solder marks on the screen with her fingertip: "Now, we have their 'handwriting.' Next, we need to investigate something—"

His gaze swept over the crowd:

"Retrieve all law enforcement records of recent years in the waters where the incident occurred to crack down on illegal vessel modifications and find information on the seized vessels."

"Then, compare the welding marks on these ships..."

As Ji Shuyun spoke, his gaze lingered on the still frame of the video sent by Xia Zhining.

"As long as the weld marks match, the murderer's identity will be revealed."

His eyes reflected Xia Zhi Ning's face on the screen, and also a certain unspoken understanding.