As it got closer to working hours, every household was either preparing or eating breakfast.
Only the doors and windows of the family on the fourth floor were tightly shut, curtains drawn.
It looked like they hadn't gotten out of bed yet.
Min-Joon went to the shop around the corner to inquire about the family.
"Old Zhu and his family have lived here for many years. To be honest, they're pitiful people."
"They had a son. Everything was fine until he suddenly got sick…"
The shop owner lowered his voice. "Mental illness."
Those words made Min-Joon's heart tighten. The image of the deceased surfaced in his mind—the wounds on the body.
Jae-Hyun frowned, clearly thinking the same thing.
"What happened to their son?"
The shop owner sighed.
"We practically watched Do-Jin grow up. He was a well-behaved and intelligent child, always excellent in his studies."
"But after entering junior high school, he became increasingly withdrawn. At first, everyone thought it was just a rebellious phase."
"Until one day, he came home completely soaked… and reeking of something foul."
"The smell made Old Zhu realize something was wrong at school."
"They went to the school to investigate. At first, the homeroom teacher claimed ignorance, but the Zhu couple insisted."
"Only after things escalated did the truth start to come out."
The shop owner hesitated, unwilling to continue.
"In any case, after that, his condition worsened. He never finished high school."
Min-Joon and Jae-Hyun exchanged a glance but asked no further questions.
They walked to the entrance of the apartment.
Just as they were about to knock, Min-Joon suddenly stopped them.
"Did you bring the reagents?"
He pointed at the doorknob—there were faint marks, as if someone had tried to wipe it clean.
Seo-Jin's eyes widened slightly.
"A mentally ill suspect… capable of committing the crime?"
"I brought it," he replied.
Before knocking, they examined the doorknob.
No one answered.
Ara collected the trace evidence and handed it to Jae-Hyun.
"You continue investigating and find out where the couple went. Min-Joon and I will return to the station."
Jae-Hyun left in a hurry.
Police Station
"New evidence! Urgent!"
Forensic doctor Jin-Woo took the sample. "I'll process it immediately."
While waiting, Jae-Hyun received a call from Seo-Jin.
"Boss, both parents have resigned from their jobs. Tae-Wook checked their records—they took their son and boarded a train to Star City around 3 a.m. yesterday."
"He tracked them along the way. They didn't reach Star City—they got off midway and switched vehicles."
"We're still tracing where they went after that."
Jae-Hyun acknowledged and ended the call. He turned to Min-Joon, who seemed deep in thought.
"You're a great fit for this department. Welcome aboard."
Min-Joon glanced at him, raised an eyebrow slightly, but didn't respond.
Footsteps approached quickly. Jin-Woo returned with the report and handed it to Jae-Hyun.
"Results are in. The trace belongs to the deceased."
Jae-Hyun straightened instantly, tapping the report. "That confirms it!"
Jin-Woo frowned. "Why are you so easily excited?"
He turned to leave, but not before giving Min-Joon a meaningful glance.
Without wasting time, Jae-Hyun called Seo-Jin.
"Prepare for arrest. Tell Tae-Wook to speed up. I'm applying for a search warrant."
Then, without turning back, he said,
"Wait for me in the car."
With the warrant secured, Jae-Hyun and Min-Joon headed out.
Soon, a message came from Tae-Wook.
"Captain, they got off at the harbor bus station—the final stop—and then took a taxi north. I tracked them, but several cameras were broken. I need more time."
Jae-Hyun wasn't surprised.
In smaller towns, surveillance systems were often incomplete. Cameras existed only at key entry points.
"I understand," he replied. "Coordinate with local police and locate them as soon as possible."
"Yes, sir!"
At the residence, the team reported their findings.
"The son's name is Zhu Do-Jin, 24 years old. His parents take him for annual checkups, but this year's hasn't been done yet."
"According to his doctor, his condition alternates between lucidity and episodes. He is capable of committing violent acts."
"We've retrieved his medical records—they're being sent to the bureau."
Seo-Jin gave Min-Joon a thumbs-up.
This newcomer was far more capable than he had expected.
The door was forced open.
Inside, the apartment was in disarray—it was clear the family had left in a hurry.
The two-bedroom unit, about 70–80 square meters, was cluttered with miscellaneous items.
Min-Joon walked straight to the side bedroom.
The door lock showed obvious signs of damage.
This was likely Zhu Do-Jin's room.
The bed edges and windowsill were padded with cloth.
By the window, a telescope stood out.
Min-Joon stepped closer. Outside the window, an extra layer of iron bars had been installed.
Given the setup, it seemed Do-Jin had exhibited self-harming behavior during episodes.
From this window, the living room of Woo-Jin's apartment could be seen diagonally below.
"Captain Jae-Hyun! There are traces of burnt food!" Ara called out.
Min-Joon paused, then walked toward the bathroom.
As he approached, a pungent odor hit him.
A mix of stale water, uncleaned surfaces, and the acrid scent of burnt fabric filled the air.
Jae-Hyun stepped forward, then stopped.
"Check the other rooms. This place…"
By the time they returned to the station, it was already past lunchtime.
Though exhausted, the team was energized by the breakthrough.
Forensic pathologist Jin-Woo entered with a rare smile.
"All test results are in. Now we just need to catch the killer."
Relief spread through the room.
Jin-Seok even let out a cheer.
Three days later
With assistance from local police, Zhu Do-Jin and his parents were arrested.
The killing had triggered a severe relapse in Do-Jin's condition.
No matter what anyone asked, he only muttered to himself—
"Be mine… they betrayed me… be mine!!!"