The Meaning of Blood Drops

Hearing this, even Sonoko, who was not particularly good at deduction, could understand the predicament Kudo Shinichi was facing:

The method was obvious at a glance, but there was simply no physical evidence that could identify the murderer.

He had worn latex gloves while committing the crime, leaving no fingerprints at the scene.

After killing the victim, he had even thrown the gloves into the toilet and flushed them away. There was no chance to collect skin flakes from anything he had left behind.

And looking around, aside from several bloody fingerprints without ridge detail, there were no other useful traces visible to the naked eye, such as shoeprints or palm prints.

"Since that's the case..."

Seeing that Kudo had reached an impasse, Suzuki Sonoko could not help looking forward even more eagerly to her idol's answer:

"Mr. Lin Xinyi, what do you think about this case?"

"Hm?" Lin Xinyi, who had remained silent the entire time, finally reacted.

He had been staring down at the corpse and the bloodstained floor, seemingly lost in a dull daze.

But when he raised his head, Sonoko suddenly noticed—

There was not the slightest trace of confusion in Lin Xinyi's eyes.

"Everything Kudo said just now was very accurate."

"Although we cannot completely rule out the possibility of premeditated murder..."

"Based on the clues currently available, it is more likely to have been a robbery that turned into murder on impulse."

Lin Xinyi began by defining the nature of the case.

His wording was more cautious, but in the end, what he meant was exactly the same as Kudo's conclusion.

Kudo preferred to start from the clues at the scene, while Lin Xinyi was more accustomed to examining the corpse:

"After a preliminary examination, there are only two visible injuries on the victim's body:"

"The first is a small area of subcutaneous bleeding at the back of the neck, caused by external impact."

"Attacking the back of the neck in this way shows that the murderer did not initially intend to kill her. He only wanted to render the victim unconscious."

"So Kudo was right. This case was most likely a robbery."

Through the injury on the victim's neck, Lin Xinyi confirmed Kudo's deduction about the case.

Then he gave Suzuki Sonoko a meaningful look.

"Come to think of it, this injury is very similar to the bruise on Miss Suzuki's neck."

"She should have suffered the same kind of attack as you."

"But unfortunately, this lady was not as alert as you were."

"She was not knocked out by the murderer's first blow, nor did she pretend to faint in time like Miss Suzuki did. As a result..."

Suzuki Sonoko: "..."

A chill ran down her spine.

The victim's experience had been exactly the same as hers. Both of them had entered an empty restroom to fix their makeup, only to be attacked from behind at the neck.

The difference was that she had reacted quickly and pretended to lose consciousness.

Otherwise, she might have been brutally murdered in this restroom, just like the victim.

"Thank goodness..."

Suzuki Sonoko muttered softly, still shaken.

Lin Xinyi continued with his analysis:

"The second injury is an oblique wound at the xiphoid process of the chest. The wound edges are neat, the wound walls are smooth, there are no tissue bridges in the wound cavity, and one wound angle is blunt while the other is sharp."

"This is an obvious stab wound inflicted by a single-edged sharp weapon."

"And judging from the pallor of the victim's skin and fingernails, as well as the amount of bleeding around the chest and abdomen..."

Lin Xinyi shifted his gaze to the victim's chest and abdomen, which had been completely soaked in blood.

"Based on the angle of entry and the length of the weapon... this stab likely cut through the pericardium, ruptured the inferior vena cava, entered the right chest cavity, pierced the lung, and ultimately caused death by hemorrhagic shock."

Having said that, Lin Xinyi directly summarized the clues and reconstructed the course of events.

"Based on the available clues, the murderer likely saw the victim enter the restroom alone to put on makeup while he was waiting for the train on the platform."

"The victim was fashionably dressed and carefully made up, so she looked like someone with money."

"The restroom was under maintenance and no one was going in or out, making it a suitable place to commit the crime."

"So the murderer acted on impulse, quietly followed the victim into the restroom, and intended to knock her unconscious by striking the back of her neck before robbing her of her valuables."

"But the victim was not as easy to knock unconscious as the murderer had expected."

"Not only did she fail to pass out, she remained conscious and prepared to call for help—perhaps even fight back."

"That made the murderer extremely nervous—outside was a crowded platform, and if he caused any commotion, he would immediately be discovered."

"So, in order to bring the situation under control, the murderer took out the short knife he had been carrying and, with almost no hesitation, stabbed this woman in the chest."

Lin Xinyi looked deeply at the woman who had died so miserably in the pool of blood.

"For such a simple, absurd reason..."

"A young life was lost."

After seeing enough cases, one could not help lamenting the fragility of life and the unpredictability of fate.

Suzuki Sonoko sensed the sorrow Lin Xinyi displayed, that feeling of grieving for someone like oneself, and she too fell silent.

But after a brief silence—

"Wait."

Suzuki Sonoko suddenly realized something.

"Isn't that basically what Kudo just said?"

The method of explanation was different, and so was how he had discovered it, but Lin Xinyi had merely repeated Kudo's deduction.

In some respects, he had even been less detailed than Kudo.

For example, Kudo had used the bloody fingerprints and tiny blood drops to determine that the murderer wore latex gloves. He knew the murderer had gone to that restroom stall after killing the victim and flushed the gloves down the toilet.

By comparison, Lin Xinyi's deduction focused more on reconstructing the details of what the victim had experienced and describing her suffering, but—

After all that explanation, the most important question still had not been answered:

"How are we supposed to identify the murderer?"

Suzuki Sonoko asked in confusion, and Kudo Shinichi also looked over with an eager, inquisitive expression.

"It's very simple."

Lin Xinyi answered casually.

"The murderer got the victim's blood on him. We just need to find the person with blood on him."

"That's not very likely, is it?"

Kudo Shinichi immediately raised an objection.

"No clothing was left behind at the scene, which means the murderer fled while still wearing the clothes he had worn during the crime."

"If blood had sprayed onto him, how could he blend into the crowd wearing bloodstained clothes?"

"And if the blood did not spray, merely flowing down the blade instead... then the murderer's hands were covered by gloves. As long as he was slightly careful, blood would never get onto his body at all."

"The gloves would not make that impossible. They would only make it much less likely."

"But that does not guarantee it never happened."

Lin Xinyi refuted him in a manner that sounded almost argumentative.

"Uh..."

Kudo had no reply.

Indeed, there was no guarantee that it had not happened.

They could try looking. Perhaps they really would find someone with blood on him.

There was nothing inherently wrong with that line of thought, but—

It sounded more like gambling on luck. It did not demonstrate the level of skill Lin Xinyi ought to possess.

If they were unlucky and found nothing, they would have wasted effort screening more than a hundred people.

And those were more than a hundred increasingly impatient Tokyo citizens. The only reason they were still here was out of respect for Mouri Ran's fists.

But Ran could not actually start hitting people, and those passengers would certainly not obediently wait forever while the investigators came up with one method after another to screen them.

If this dragged on too long and more than a hundred citizens began making a scene, even the Tokyo Metropolitan Police Department would have no choice but to let them go.

So they still needed to come up with an accurate and effective screening method as quickly as possible.

That was what Kudo was thinking.

But then, unexpectedly, Lin Xinyi immediately provided evidence for his claim.

"The possibility of blood getting on him exists."

"And I can prove that the murderer definitely got the victim's blood on his body."

"Take a look at those tiny blood drops on the floor—"

As he spoke, Lin Xinyi pointed at the long trail of tiny blood drops on the ground.

Those scattered drops extended from where the victim had collapsed all the way to the restroom stall where the murderer had discarded the knife.

Obviously, just as Kudo had deduced, these were blood drops that had fallen as the murderer carried the knife to the stall after killing the victim.

But Lin Xinyi saw something more in those tiny drops.

"This type of bloodstain is called a drip stain bloodstain in trace evidence analysis."

"A drip stain bloodstain is formed when blood falls onto the surface of an object under the force of gravity."

"This type of stain is generally circular or nearly circular."

"However, in most cases, the surface onto which the blood falls is not smooth."

"So 'spines' appear around the edges of the drip stain."

(It probably looks something like this:)

As he spoke, Lin Xinyi motioned for Kudo and Sonoko to come closer, crouch down, and examine the tiny blood drops on the floor at close range.

Sure enough, they both noticed that around the circular blood drops were visible fine blood spikes, radiating outward in all directions like starlight.

At that point, Lin Xinyi added further:

"Look more closely. Aren't the spines on these blood drops mostly longer on one side and shorter on the other?"

"They really are... It's not very obvious, but you can still see that the spines on the left and right sides of a blood drop are different lengths."

Like she had discovered a new continent, Miss Suzuki exclaimed:

"Why is that?"

"Because these blood drops fell while the murderer was moving."

Lin Xinyi explained carefully:

"For blood drops that fall vertically while stationary, the spines around them are relatively even in size and length."

"But at the time, the murderer was walking toward the restroom stall, so the blood drops falling from his body carried horizontal velocity."

"When those blood drops hit the ground, more blood gathers in the direction of that velocity, and the spines on that side become longer."

"In other words—"

Lin Xinyi paused, emphasizing the key point.

"The side with the longer spines indicates the direction in which the murderer was moving at the time."

"For example, the long spines on this blood drop point toward the restroom stall, proving that the murderer was indeed carrying the bloody knife toward the stall."

"This..." Suzuki Sonoko looked rather confused.

"What use is knowing that?"

"Didn't Kudo already deduce that the murderer went to the stall after killing her to dispose of the weapon and gloves?"

"No. It is very useful."

The one who spoke up to disagree was Kudo Shinichi.

He stared intently at the floor, his eyes utterly focused.

"I understand what Mr. Lin Xinyi means now."

"The direction of the long spines on a blood drop can reveal the direction in which the murderer was moving at that time."

"And the blood drops here..."

Kudo Shinichi pointed to a particular blood drop on the ground.

"Not all of the blood drops have long spines pointing toward that restroom stall."

"Several of them have long spines along their edges pointing in the exact opposite direction from the others!"

"Uh?" Suzuki Sonoko had already lost the thread.

"Remember, the long spines on a blood drop point in the direction the murderer was moving at the time."

Seeing that Miss Sonoko was getting increasingly bewildered, Lin Xinyi emphasized the point once more.

"And the fact that several drops have their long spines pointing in the opposite direction means..."

"Those drops are different from the others. They did not fall while the murderer was heading toward the restroom stall."

"They fell while the murderer was leaving that stall and returning toward the sinks along the same route, which is why their long spines point in the exact opposite direction from the other drops."

"In other words—"

"After the murderer disposed of the weapon in the stall and threw the gloves into the toilet..."

"Blood was still falling from his body!"

"The blood that fell at that point was not on the gloves or the weapon at all. It had gotten directly onto the murderer's body."

Finally, Lin Xinyi summarized seriously:

"So it is not difficult to imagine that the gloves did not completely block the victim's gushing blood."

"That blood must have flowed onto the murderer's arm, and as long as we find the person whose arm is stained with the victim's blood, we can identify the murderer."

"That's true..."

"However..."

Kudo quickly found a flaw in Lin Xinyi's idea.

"After disposing of the weapon and gloves, that guy should have washed his arm at the sink."

"Otherwise, if there were conspicuous bloodstains on his arm, he would have had a hard time blending into the crowd."

"That doesn't matter."

Lin Xinyi smiled very calmly.

"It would not matter even if he washed his hands perfectly clean."

"As long as he really got blood on himself, I will definitely be able to drag him out!"