4:38 a.m.

SID Operations Room.

No one had left.

The lights were white.

White like a hospital.
White like an interrogation room.

The files of the four cases
hung side by side on the main screen.

Lin Bing.
Hong Yu.
Tan Xin Yi.
Su Mei Mei.

Four young faces.

Four nearly identical seated postures.

Four locations.

Like four nails,
driven one by one
into the same invisible board.

I remained standing.

I did not sit.

At a stage like this in a case,
the moment you sit down,
your thinking tends to slow.

Chang Hsin-Yan stood on the left,
arms folded,
eyes fixed on the screen.

Lee Wai Hing sat at the long table,
enlarging the scene photos one by one.

Yim Bing stood at the back,
studying the map.

Tan Chih Lin’s fingers never stopped,
pulling layer after layer of data to the surface.

Kim Min Jung had already projected
the street models of all four crime scenes
onto the side screen.

Dr. Cheng Kok Ming stood by the whiteboard,
having just written down the latest forensic reference numbers.

I spoke.

“Start with the first case.”

Tan Chih Lin tapped twice on the keyboard.

The main screen changed.

The first photograph appeared.

A young woman,
seated by the outer steps of an academic building
at East City University.

Leaning against a pillar.

Head tilted.

Eyes half open.

An unnaturally quiet expression on her face.

The file appeared beside her image:

Lin Bing.
Twenty-two years old.
Third-year Computer Science student, East City University.
Time found: January 14, 2024, 11:42 p.m.
Location found: East platform stairway, Science Building, East City University.

The room was silent for two seconds.

No one spoke.

Because the first case
had looked too much like an accident.

And precisely because it looked so much like one,
it had been allowed to pass.

I looked at the photograph.

“How was it classified at the time?”

Dr. Cheng answered.

“Initially handled as sudden cardiopulmonary failure. No obvious external injuries, no clear toxicological markers, no struggle, no signs of assault. The scene was not pursued as a criminal case.”

“And the autopsy?”

“It was done. But at the time, the ‘abnormal scent’ was not treated as a central direction. It was mentioned only in a note: faint fragrance present at the scene, possibly the victim’s personal perfume or environmental transfer.”

I said nothing.

I just looked at that line.

A note.

A lot of cases
die inside notes.

Chang Hsin-Yan suddenly spoke.

“She doesn’t look like someone who struggled before sudden death.”

I turned to her.

“Go on.”

“Look at the downward angle of her shoulders, the natural fall of her arms, the level of relaxation in her legs. She didn’t collapse in pain. It’s more like her… consciousness was removed.”

The room fell quiet for a moment.

“Consciousness was removed.”

It was not a pleasant phrase.

But it was precise.

I lifted my chin slightly.

“Second case.”

The screen changed.

This time,
it was a hotel.

West City.
The external concierge stairway of the Westin Hotel.

The night lighting was warmer.

The ground was spotless.

The girl was seated in the same structural position.

Beside a stairway.

By a pillar.

Leaning back.

Head tilted.

Motionless.

The file appeared:

Hong Yu.
Twenty-one years old.
Third-year Computer Science student, West City University.
Time found: six months ago, 10:16 p.m.
Location found: external concierge stairway, Westin Hotel, West City.

Lee Wai Hing enlarged the image.

“No scuff marks on the shoes. No obvious pulling on the skirt hem either. That means before she went down, there was no significant self-rescue movement.”

“The surveillance?” I asked.

Kim Min Jung had already pulled it up.

The hotel exterior camera
captured Hong Yu sitting down at 10:07 p.m.

She was not dragged there.

She was not supported there.

She walked there by herself,
and sat down by herself.

No panic.

No disorder.

In fact,
she seemed calm.

At 10:09,
a hotel attendant passed at a distance,
glanced at her,
and suspected nothing.

By 10:12,
she had become completely motionless.

At 10:16,
a second staff member approached
and found something was wrong.

Yim Bing spoke from the map wall.

“This position is not far from the hotel’s main entrance, but it also happens to fall into a side-angle of the camera. Not the clearest view, but not a full blind spot either. The location was chosen carefully. Not randomly.”

I nodded.

“He knows where people can be seen,
but details cannot be clearly seen.”

“Exactly,” said Yim Bing. “This wasn’t improvised. It was pre-scouted.”

I looked at Hong Yu’s photograph.

The second case
already did not feel like an accident.

But at the time,
it had still not been formally connected.

Why?

Because a city produces too many incomplete signals every day.

Each department
only receives its own fragment.

No one puts the entire puzzle

onto the same table.

Not until the fourth case.

Only then
was the table finally overturned.

“Third case,” I said.

The main screen changed again.

This time,
I recognized the place immediately.

East City.
Yokoso Shopping Centre.

Unlike the first case,
this place was more commercial.

Brighter.
Still carrying the lingering trace of public foot traffic.

But the girl in the photograph
was still quiet in a way that did not belong to the living.

The file appeared:

Tan Xin Yi.
Twenty-two years old.
Third-year Computer Science student, East City University.
Time found: one month ago, 12:21 a.m.
Location found: East Wing stair platform, Yokoso Shopping Centre, East City.

Kim Min Jung placed the third case surveillance footage beside it.

Tan Xin Yi entered the frame at 12:13 a.m.

No one was beside her.

She walked to the pillar.

Paused for two seconds.

As if she had heard something.
Or smelled something.

Then
she sat down slowly.

Back against the pillar.

Head tilted slightly to the right.

The movement was so light
it looked like she was simply taking a rest.

After 12:15,
she never moved again.

I narrowed my eyes.

“Stop. Back three seconds.”

The footage rolled back.

I stared at the moment she entered the frame.

“Again.”

Kim Min Jung replayed it.

This time,
Chang Hsin-Yan stepped two paces closer too.

“She wasn’t here to wait for someone,” she said.

“Why?” I asked.

“A person waiting for someone checks their phone, watches the entrance, scans intermittently. She does none of that. Her attention isn’t external. It’s as if she’s being led here by some internal sensation.”

“Internal sensation?” Lee Wai Hing looked up.

Chang Hsin-Yan kept her eyes on the screen.

“Dizziness. Dissociation. Or some kind of inducement that makes her feel she has to sit down.”

I did not answer.

Because in my mind,
I was already overlaying all four sequences.

Four girls.

All young.

All quiet.

All walking themselves into position.

Sitting down by themselves.

And then,
as if pressed by the same invisible hand,
stopping.

I spoke slowly.

“List the shared points across all four cases.”

Tan Chih Lin projected them immediately.

Line by line,

they appeared.

Shared characteristics:

1. All victims were university students.
2. All four were Computer Science students.
3. Their ages clustered between twenty-one and twenty-two.
4. All were alone at the time of the incident.
5. All were seated by stairways, leaning against pillars or fixed vertical structures.
6. No obvious external injuries.
7. No obvious signs of struggle.
8. Personal belongings intact.
9. Similar abnormal scent residue present at all scenes.
10. All four locations were semi-public spaces, combining visibility with blurred surveillance angles.

Ten lines.

Each one
felt like driving another needle into the air.

Yim Bing spoke first.

“The locations aren’t completely hidden. In other words, the offender doesn’t mind the body being found.”

“He may even need it to be found,” I said.

Chang Hsin-Yan turned to me.

I continued.

“If the body isn’t discovered for too long, environmental airflow, residue volatility, and time distortion all start to affect the scene. What he may want is not to hide the result, but to have the result seen at a certain point in time.”

Dr. Cheng Kok Ming nodded.

“That way, what we collect reflects the real effect he wanted to test.”

The room went still for half a second.

The word test
had appeared on the table
for the first time in a concrete way.

Chang Hsin-Yan slowly turned back to the screen.

She studied the faces of the four dead girls.

For a long moment.

Then she said:

“This is not random.”

No one interrupted.

Because everyone was waiting for the next sentence.

She gave it.

“This is selection.”

The moment those two words landed,
even the air seemed to grow colder.

Lee Wai Hing frowned.

“Selection for what?”

“For targets,” said Chang Hsin-Yan. “Maybe background. Maybe aptitude. Maybe habits. Maybe some common exposure source they themselves never noticed. But he is not choosing random pedestrians. Four victims, all Computer Science students. Two universities, three locations, four different time gaps, yet the same pattern. That kind of overlap is not luck. That is filtered condition selection.”

While she spoke,
Tan Chih Lin was already pulling up the victims’ digital lives.

Course records.
Club records.
Login habits.
Forum accounts.
Competition rosters.
Device brands.
Application usage frequencies.

The information poured down like a waterfall.

“I have a preliminary overlap,” he said.

“Talk.”

“All four were active on several similar tech forums and coding communities. Two of those forums look public on the surface, but they have invitation-only channels in the backend. All four accessed them.”

I looked at him.

“The same channel?”

“Still verifying. But the overlap rate is high.”

Kim Min Jung added on.

“There’s something else. In the week before each incident, all four entered high-footfall locations with similar ventilation structures. Malls, hotel spaces, university buildings—they all had atrium return flow or semi-enclosed air circulation patterns.”

Silence.

Short.

But heavy.

I walked to the side screen
and studied the models of the four locations.

The stairs.
The pillars.
The airflow.
The camera angles.
The foot traffic lines.

Suddenly,
they no longer looked like four places.

They looked like four test chambers.

“This is not simple murder.”

I said it.

No one moved.

I heard the coldness in my own voice.

“The killer is observing reactions.”

I turned,
looking at the four young faces.

“He doesn’t only want them dead.”

“He is testing.”

This time,
no one argued.

Because every clue
was pushing us to the same place.

The first case
looked like a trial.

The second,
a calibration.

The third,
a confirmation.

And the fourth—

a declaration.

I returned to the main screen.

“Pull everything from the month before the incidents for Lin Bing, Hong Yu, and Tan Xin Yi. Every perfume sample, free gift, campus event, tech-forum invitation, courier delivery, offline attendance list. Dig it all out.”

“Yes,” Tan Chih Lin answered.

“Min Jung, get me the airflow system maps for all four locations. I want to know how this scent could remain in an environment if it wasn’t deployed at close range.”

“Understood.”

“Lee, reopen the evidence seal on the first three cases. Clothing, hair, cuffs, bag straps, phone cases. Anything that could have retained residue—test it again.”

“Alright.”

“Yim Bing, build the scene model on the assumption of an organized deployment team. I want to know the minimum number of people needed to set, observe, and withdraw without disturbing the scene.”

“I’ll have it tonight,” she said.

“Hsin-Yan.”

She looked at me.

“If this is selection, what is the most likely selection criterion?”

She did not answer at once.

She simply looked back at the four faces.

After a while,
she said:

“Not who is easiest to kill.”

“It’s who is suitable for testing.”

No one spoke.

Because that sentence
was colder than death itself.

Suitable for testing.

That meant
there could be more.

Not just four.

Maybe never just four.

I walked to the window.

The sky was beginning to grey.

The city was about to wake.

Traffic would rise.

Malls would open.

Students would enter classrooms.

Working people would hurry down the streets carrying coffee.

They would not know
that something
had already entered the city.

It smelled good.

It was invisible.

Untouchable.

It did not shout.

It did not make noise.

And yet it could quietly
switch a person off.

I stood with my back to the others,
looking at my reflection in the glass.

Then I said:

“From this point on, this is not four homicide cases.”

I turned around.

“This is a preliminary test against the city.”

The light from the screens
fell across everyone’s faces.

No one thought I was overstating it.

Because we all knew—

if the other side was truly selecting,
truly testing,

then next time,

what he wanted
would not be just one girl by a stairway.