The Gray Thread

The stairwell door closer and Baek Sangho's case seemed to have passed through the same place, but they didn't tell the same time.

Seojin laid the transparent baseline back over the eighth floor stairwell threshold. Dohyun lifted the case's wheels and set them against the threshold. The wheel width matched the wear on the inside of the door, but for the case to pass through, the door would have needed to open to 74 degrees.

"What angle was the door at that day?" Minwoo asked.

"The sensor only records opening events." Dohyun answered. "There's no opening angle."

Seojin looked at the scratch on the door closer. The scratch wasn't at a height that would form when the door was fully open. It was a mark left when the wheels were pushed from inside to outside, with the door half open.

"The case might not have gone out. It might have come in."

"Then what about the person?"

"A person might have held the door first, with the equipment following."

Minwoo checked below the stairs. There was damaged paint on the railing leading down to where Han Jaehee had fallen, but it didn't match the height of the case's handle.

"A trace of moving the body?"

"It's possible, but other heavy equipment could make the same trace."

Seojin attached a possibility to every sentence now. Minwoo no longer felt frustrated hearing that word. Instead, he asked for a counterexample.

"If it were the body, what would need to be different?"

"The gray grains on the sole of the shoe would need to be on the same path as the case wheels. And the height of the threshold scratch would need to match the shift in a person's center of gravity."

Dohyun laid the photo of the body's shoes next to the photo of the case wheels. The grains from the shoe were more concentrated inside the threshold. The fluorescent powder from the case was more concentrated outside it.

"Not the same direction."

"Then the hypothesis that the case was used to move the body weakens."

Seojin drew a small parenthesis next to "Move?" She revised "body or equipment" to "equipment, more likely."

That afternoon, the Gray Room reproduced only the exterior scratches without opening Baek Sangho's case. The facilities contractor's supervisor said the case had been used for server replacements across several buildings. It became possible the fluorescent powder on the case wheels had come from a different site.

"Then is today's case meaningless?" Minwoo asked.

"Not meaningless. But we can't assume it belongs to this one case."

Seojin zoomed in on the rubber section of the case handle. A small blue fiber was caught inside it. Determining whether it matched the fiber family from Han Jaehee's coat would require a separate analysis.

Han Gyeongmin didn't consent to the analysis.

"The case belongs to the contractor."

"We only need to check the external contact surface, within a limited scope." Yeoreum said.

"Once that check is done, a name will get attached again."

"We can record the physical properties without attaching a name."

Gyeongmin looked at Seojin.

"Do you actually do that?"

"I couldn't, on the first day."

The answer didn't change the expression on Han Gyeongmin's face, but it changed the direction of the conversation.

Seojin compared the impression from the case wheels to the impression under the server rack. The lengths were similar, but the depths differed. The server rack had been pressed into the floor for a long time. The case's mark was from a single slip during transport.

"The server rack and the case didn't move the same way in the same place."

"Someone could have pushed the server rack and dragged the case."

"That possibility remains. But the evidence that the two objects moved together at once has weakened."

Minwoo looked at the scene reconstruction photos and said,

"So it might not be the tool used in the crime, just a trace of someone coming and going at the scene."

"That's still a hypothesis too."

Around lunchtime, Kim Dabin came to the Gray Room. She didn't use Han Gyeongmin's name, calling him "Director." It was a form of address that hadn't changed since the first day.

"The line in the text, 'not the elevator,' that was really written by my sister."

"Why are you telling us now?"

"Yesterday I was only thinking about hiding the name underneath it. But now that equipment has come up too, I felt like I had to say who she was trying to avoid."

"Who?" Minwoo asked.

Dabin didn't answer right away.

"I won't say the name. But I can tell you she didn't use the stairs."

Seojin checked the scope of that statement.

"Did you see it directly?"

"I saw a record my sister left."

"The original?"

"It's part of a voice message she sent me. I'm not going to release the original."

Yeoreum cut in.

"Then let's confirm only what's observable. Was there a sentence saying she didn't use the stairs, or does it mean she didn't hear the sound of movement?"

Dabin's hand froze over her phone.

"She said, 'the door closed twice.' Not the elevator door. The stairwell door and the building entrance."

Seojin recorded the sentence. It wasn't evidence that Han Jaehee had climbed the stairs. It was an observation that the stairwell door had moved twice.

"Can you let us hear that message?"

"No."

"Can you just tell us the time?"

Dabin wrote down only the time the voice message was received. 05:33:58. It was a number that could be compared against the sensor's closing event without duplicating the original.

Dohyun opened the server log.

"Sensor closing was 05:32:31. The message was sent 1 minute 27 seconds later."

"It could have been sent after the sound of the door closing twice."

"Right. To fix the order, we'd need the internal timestamp of the original audio."

Dabin shook her head.

"That's not possible."

Seojin accepted her refusal. It wasn't that the investigation had stalled for lack of an original. It was a moment to redefine what could be said without one.

At 5 p.m. that day, Han Gyeongmin opened the sealed storage room in the management office. He hadn't handed over the key to that room before, but he said he would personally check the list of discarded equipment left inside.

"Why show us now?" Minwoo asked.

"If I opened that room from the start, I was afraid you'd check even where the child was hiding."

"The child's name and the room's location can be kept separate." Yeoreum said.

"I know. But I couldn't trust that."

Gyeongmin handed over the equipment list from inside the storage room. Two server cases, one mobile terminal, four sensors slated for disposal. The equipment Baek Sangho had tried to recover wasn't on the list.

"There's another case missing from the list."

Seojin looked at the blank line on the list. The absence of the equipment didn't say where it had gone. But it did confirm that someone had had the authority to edit the list.

On the storage room floor were narrow wheel tracks, different from the server rack's. Not from a case, but a trace of a small cart being used.

Seojin added a line next to "Move?" in her notebook.

"Might not be the case."

The ability's misreading hadn't disappeared. But faced with an independent physical trace, it had turned into a smaller question. Not whether a person had been moved, but who moved what, and why it was missing from the list.

The blank line on the storage room list hadn't been filled in by Han Gyeongmin himself. He contacted the management company to request past revisions, and said he wouldn't write anyone's name down until that material arrived.

Minwoo was suspicious of that attitude.

"He might be trying to buy time."

"He might be." Seojin said.

"Then why wait?"

"Because it might be the only record that can confirm who edited the list."

"What if the equipment disappears before that record arrives?"

"That's why we sealed the storage room door."

Minwoo didn't ask further. He hadn't done it because he trusted Gyeongmin's cooperation. He'd created a state that wouldn't change even without it.

Han Yeoreum looked at Seojin's notebook and said,

"Dabin's message belongs in the case questions. The original doesn't."

"I know."

"Don't let information we don't have stand in for interpreting a person's actions."

Hearing that, Seojin erased a blank space in her notebook. It was where she had been about to write the hypothesis that the voice message contained the direction of the crime. Instead she wrote, "Statement that the door closed twice, internal timestamp unconfirmed."

Yeoreum read her sentence back without correcting it.

"Written this way, the next reviewer might demand the original."

"They might. But I'll also note that Dabin can refuse."

"What if the refusal delays the investigation?"

"Then I record the delay and the reason for the refusal separately."

Yeoreum was silent for a moment. Then she wrote her own name in the person-in-charge column of the disclosure restriction sheet. A signature acknowledging the refusal to view the original.

At 7 p.m., the revised past equipment list arrived from the management company. The list before revision had one small mobile cart. It was the only item missing from the revised list. The deletion time was 23:17 the night before Han Jaehee died.

Minwoo tried to contact Baek Sangho right away, but Seojin stopped him.

"We can't yet say the cart was used in the crime."

"But it was erased from the list."

"We need to confirm who erased it and why."

Dohyun compared the cart's wheel width to old equipment photos. The width matched the narrow track inside the stairwell. But the cart could also have been used on other floors of the building.

Seojin wrote down three possibilities. Transporting server equipment, moving waste, moving Han Jaehee's belongings. None of them explained the person's whereabouts directly.

Han Gyeongmin looked at the last line of the revised list and said,

"This cart doesn't belong to the outside contractor."

"How do you know?"

"The building management team used it. I submitted the disposal request."

"When?"

"The day after the incident."

Seojin wrote down the date. Gyeongmin's statement explained that the cart existed on the day of the incident, but it didn't explain why it was missing from the list.

Minwoo said,

"Tomorrow we check where the cart is stored."

"It might already have been disposed of by then."

"Then we check the disposal records."

Seojin laid the stairwell threshold and the cart's width over the same photo. She didn't conclude the cart had passed through. She noted that its width would have allowed it to.

As the night deepened, the sealed equipment list and the disclosure restriction sheet sat side by side in the Gray Room's hallway. One protected the movement of an object. The other protected a person's choice.

Beneath the word "stairs," Seojin wrote a third line.

"Confirm the route of movement, not the location."