Chapter 10 — Calls are not allowed to be hung up

After the fourth call ended, Dan did not return to his seat immediately. She brought the notebook and the drive containing all the recordings, sat down in the empty chair next to Anh Tuyet's desk, and they both stared intently at the screen like two investigators dissecting a scene they had never been to.

— I listened to this part again for you, right in the first minute of the second call.

Anh Tuyet pushed the headset over to Dan, her finger lightly tapping the screen where the audio cursor was stopping at a specific point on the recording waveband. The two of them sat close together at Anh Tuyet's desk, the screen light casting a pale blue halo on both of their faces in the room, which was much darker than a few hours ago, when most of the ceiling lights had been adjusted to energy-saving mode at night.

Dan put on headphones, closed his eyes, focused all his senses on the ninety-second audio clip that was playing, trying to filter out all other noise in his mind so that only the thinnest layer of sound remained hidden deep beneath the child's voice. At the forty-second mark, behind the child's whispering voice and the karaoke music echoing through the wall, there was a very small sound, almost mixed into the background noise, a long, deep hum, repeated exactly three times evenly spaced.

— Have you heard?

— I heard it. Like a bell.

— I thought so too, but when I first heard it I didn't pay attention because it was too small and mixed into the karaoke sound.

Anh Tuyet opened another window on her computer and quickly typed in a search in the internal directory of religious establishments in the Dong Lam ward area that the center still keeps for coordination in cases where community notification is needed.

— Dong Lam area has only one church, Vong An parish, located about three hundred meters from Vong Thuy alley as the crow flies. That church had a habit of ringing at fixed times, five in the morning, twelve in the afternoon, six in the evening, and had a short bell ringing for late mass at about eleven thirty-five every Friday night.

— Today is Friday.

- That's right.

Dan looked back at the time of the second call, eleven thirty-five minutes, which coincided almost perfectly with the bell ringing for late night mass at Vong An parish. She felt a rush of excitement run down her spine, a rare feeling she had only experienced a few times in her eight years of working, when disparate pieces of a puzzle suddenly fit together into a clear image.

— Three hundred meters from Vong An parish, plus the location near the eastern train tracks, plus the only five-story elevator-less apartment building in the area with a suitable structure... — Dan muttered, typing quickly on the keyboard to redraw the overlapping circles on the digital map. — It all points to exactly one point.

Anh Tuyet looked at the screen, where three circles of different radii, one from the broadcast station location data, one from the estimated distance to the parish based on the intensity of the bell sound, one from the distance to the tracks based on the clarity of the train whistle, intersected in a small area that coincided with the location of the Lam Dien apartment building on the map.

— This is no longer speculation, Dan. This is an acoustic triangulation, no less accurate than the radio triangulation used by navigation systems.

— But it still doesn't tell me exactly which apartment.

— Yes, but it's strong enough to convince anyone with a logical mind, including Mr. Long.

Anh Tuyet stood up, went to get a printed piece of paper with an enlarged map of the Dong Lam area, spread it on the table, used a red pen to circle each landmark: Vong An parish, the nearest railway line, and the location of the Lam Dien apartment building located between those two points, no more than two hundred meters on each side.

— Looking at a paper map like this, it's much easier to convince others than looking at overlapping circles on the screen. People still believe more in what they can hold in their hands.

— You're right. Let me print another copy of the recording with the bell ringing, clearly marking the time, so that if I need to present, I have all the images and sounds.

Dan reopened all four recordings, arranging them chronologically on a new dashboard, each call accompanied by confirmed details: call one, nine seconds, no additional location information; round two, twenty-two seconds, uncle shouted, high floor, stairs, Vong An parish bell at eleven thirty-five; round three, one minute and forty-seven seconds, fourth floor, no elevator, smell of cigarette smoke in the hallway; four minutes and twelve seconds, the mother was seriously injured, the dog barked intermittently, the train whistled at one seventeen.

She realized something else: all four calls came from the same subscriber number, without an officially registered name, most likely an unofficial prepaid phone, a type of phone popular in families with tight economic circumstances, often only used for basic communication without fully registering personal information as prescribed. That small detail, although it does not help with further location, paints a clearer picture of the child's family's living situation.

— Four calls, four puzzle pieces, one location. — Anh Tuyet nodded slowly, then glanced at the clock. — It's one thirty in the morning. If Mr. Vinh had passed by the area, perhaps he was about to respond.

At that moment, Dan's personal cell phone, the one she kept on vibrate in her desk drawer reserved for calls outside of work, vibrated for a moment. She pulled it out, saw Vinh's name appear on the screen, quickly pressed to listen, her heart beat much faster in just half a second waiting for the connection.

— Mr. Vinh, is there anything?

— I just passed by Lam Dien apartment twice. It looked quiet from the outside, most of the windows had their lights turned off, only one or two houses were still lit but no unusual noises were heard from the street.

Hearing that, Dan's heart sank a little, but she did not let disappointment control her, because she clearly understood the limitations of just observing from outside a closed building.

— Do you see any apartments on the fourth floor, the side facing the train tracks?

— There are two houses on that side, one has the lights completely turned off, the other has a dim light coming from the door, possibly a night light or a hallway light in the house. He didn't dare stand there for too long, for fear of attracting attention if someone was actually on guard.

— Did you hear the dog barking?

— Yes, a certain domestic dog barked a few times as he passed by, intermittently, not very fiercely.

That detail completely matched the child's description, making Dan even more certain about the direction of her inference, even though she knew the level of certainty in her mind was still far from the level of "legal basis" that Long required, the gap between a firm belief and evidence that could stand up to the disciplinary council.

- Thank you very much. Can you continue to keep an eye on that area, especially that dimly lit apartment?

— Okay, I'll come back for another round after I finish handling a few other things during the shift. But Dan, I'll say it again, if there's nothing more clear, in the morning I'll still have to finish the shift without doing anything more than that.

- I know. Thank you.

Dan hung up the phone, turned to Anh Tuyet, and narrated the entire content of the call. After listening, Anh Tuyet lightly tapped the tip of her pen on the table in a familiar rhythm. Her eyes looked far away toward Long's office, where the light was still on even though it was past one thirty in the morning.

— With everything I have now, I think it's time to go back to see Mr. Long again.

— I think so too. But this time I'm afraid it's not enough.

— It's not enough or not enough, Dan. That I have to fight again, no matter what the result is.

Dan folded up the paper map, sandwiched it with the notebook and notepad summarizing the four calls, feeling the familiar heavy feeling of preparing to enter a conversation that she knew she could hardly win with pure reason. But she also knows that every minute of hesitation right now could be a minute that cannot be taken back.

— Will you come with me?

- Of course. But this time, let me say a few sentences first, giving him time to calmly listen to everything before reacting.

The two of them stood up almost at the same time, looked at each other in wordless agreement, then walked towards the end of the duty room, where the small office door was still slightly open as if waiting for another discussion.