The Meaning of the Drip Stain Bloodstain

## The Meaning of the Blood Drops

Even though she wasn't particularly skilled at deduction, Sonoko could understand the dilemma Kudo Shinichi was currently facing:

The method was obvious at a glance, but there was no physical evidence to pinpoint the culprit.

He wore latex gloves during the crime, leaving no fingerprints at the scene.

After killing the victim, he even flushed the gloves down the toilet, leaving no chance to collect skin cells from any items he left behind.

And looking around, besides a few bloody fingerprints, there were no shoe prints, palm prints, or other useful traces visible to the naked eye.

"In that case—"

Seeing that Kudo was already in a difficult spot, Suzuki Sonoko couldn't help but anticipate her idol's answer even more:

"Mr. Lin Xinyi, what do you make of this case?"

"Hmm?" Lin Xinyi, who had been silent all this time, finally reacted.

He had been staring down at the body and the blood-stained floor, as if lost in thought.

But now, as he looked up, Sonoko suddenly noticed—

There was no confusion whatsoever in Lin Xinyi's eyes:

"Everything Kudo just said is very accurate."

"While the possibility of premeditated murder cannot be entirely ruled out,"

"Based on the current clues, it's more likely a robbery and murder committed on impulse."

Lin Xinyi began by defining the nature of the case.

And although his words were more cautious, ultimately, what he expressed was completely consistent with Kudo's.

It was just that Kudo preferred to start from the clues at the scene, while he was more accustomed to observing the body:

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

"The first is a small area of subcutaneous hemorrhage on the back of the neck, caused by blunt force trauma."

"An attack of this nature to the back of the neck suggests the killer didn't intend to kill at first, but merely to incapacitate the victim."

"So Kudo is right; this case is most likely a robbery."

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

Then, he gave Suzuki Sonoko a meaningful look:

"Speaking of which, this injury on the victim is very similar to the bruise on your neck, Miss Suzuki."

"She must have suffered the same attack as you."

"But unfortunately, this lady wasn't as quick-witted as you."

"She wasn't knocked out by the killer's first blow, nor did she feign unconsciousness in time like you, Miss Suzuki, and as a result—"

Suzuki Sonoko: "..."

A shiver ran down her spine.

This victim's experience was, in a way, identical to hers: both went into an empty restroom to apply makeup, and both were attacked from behind in the neck.

It was just that she reacted quickly, pretending to faint.

Otherwise, she would probably have been brutally murdered in that restroom, just like this victim.

"Thank goodness, thank goodness."

Suzuki Sonoko murmured softly, still feeling a chill of fear.

Lin Xinyi, meanwhile, continued to elaborate on his findings:

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

"This is a clear stab wound from a single-edged sharp object."

"And judging by the victim's pale skin, her fingernails, and the amount of bleeding in her chest and abdomen—"

Lin Xinyi's gaze shifted to the victim's chest and abdomen, which were completely stained with blood:

"From the angle of entry and the length of the weapon, this stab wound likely pierced the pericardium, leading to a rupture of the inferior vena cava, entering the right thoracic cavity and puncturing the lung, ultimately causing death due to hemorrhagic shock."

After saying this, Lin Xinyi directly summarized the clues, reconstructing the process of the case:

"Based on the available clues, it's highly probable that the killer saw the victim, who had entered the restroom alone to put on makeup, while waiting for a train at the platform."

"Because the victim was fashionably dressed and meticulously made up, she appeared to be wealthy."

"And the restroom was under repair with no one coming or going, making it suitable for the crime."

"So the killer acted on impulse, quietly followed the victim into the restroom, intending to attack her from behind in the neck to knock her out, and then rob her of her valuables."

"However, the victim wasn't as easily knocked out as the killer had imagined."

"Not only did the victim not fall unconscious, but she remained awake and prepared to call for help, or even resist."

"This made the killer very nervous—because just outside was a busy platform, and if he caused a commotion, he would immediately be discovered."

"So, to quickly control the situation, the killer took out a short blade they had on them and, almost without hesitation, stabbed the victim straight through the chest."

Lin Xinyi gazed deeply at the woman who had tragically died in a pool of blood.

"All for such a simple, ridiculous reason," he said.

"A young life was lost."

Seeing so many cases always made one lament the fragility of life and the unpredictability of fate.

Suzuki Sonoko sensed Lin Xinyi's shared sorrow and also became quiet.

However, after a brief silence, "Wait,"

Suzuki Sonoko suddenly reacted.

"Isn't this pretty much what Kudo just said?"

Although the way it was told was different, and the discoveries were made through different means, what Lin Xinyi was saying now was essentially just a repetition of Kudo Shinichi's deductions.

In fact, in some places, he wasn't even as detailed as Kudo.

For example, Kudo had also confirmed through the bloody fingerprints and small bloodstains that the killer was wearing latex gloves, and knew that after killing the victim, the killer went to the toilet stall and flushed the gloves down the toilet.

In contrast, Lin Xinyi's deductions focused more on reconstructing the details of what the victim experienced before death, describing the suffering the victim endured, but…

After all that explanation, the most crucial question remained unanswered:

"How exactly do we identify the killer?"

Suzuki Sonoko asked, puzzled, and Kudo Shinichi also looked at Lin Xinyi with an inquisitive gaze.

"It's simple,"

Lin Xinyi replied very casually.

"The killer got the victim's blood on them. Just find the person with blood on their body."

"That's unlikely, isn't it?"

Kudo Shinichi immediately raised an objection.

"There were no clothes left at the scene, which means the killer escaped directly while wearing the clothes they committed the crime in."

"If blood splattered and got on them, how would the killer blend into the crowd wearing those blood-stained clothes?"

"And if there was no blood splatter, and it just flowed down the blade… then the killer's hands were covered by gloves. As long as they were careful, their body wouldn't get any blood on it at all."

"No, having gloves on just makes the chances of getting blood on them very small."

"But that doesn't guarantee it didn't happen at all."

Lin Xinyi retorted in a somewhat argumentative manner.

"Uh…"

Kudo Shinichi was speechless.

Indeed, there was no guarantee it didn't happen.

So, he tried to look for it, maybe he really would find someone with blood on them.

This line of thought wasn't wrong, but…

It was more like relying on luck, and it didn't showcase Lin Xinyi's expected level of technical skill.

If they were unlucky and didn't find anything, they would have wasted the effort of checking over a hundred people for nothing.

And those were over a hundred impatient Tokyo citizens. The fact that they were still there was already thanks to Mouri Ran's influence.

But Ran wouldn't actually use force, and those passengers would certainly not wait patiently forever, allowing investigators to come up with a method and then try to check them one by one.

If the delay was too long and over a hundred citizens started causing a commotion, even the Tokyo Metropolitan Police Department would have to release them.

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

Kudo Shinichi was thinking this.

But then, unexpectedly, Lin Xinyi immediately provided evidence to support his point:

"The possibility of getting blood on them exists."

"And I can prove that the killer must have gotten the victim's blood on their body."

"Look at those small bloodstains on the ground—"

As he spoke, Lin Xinyi pointed to the long trail of small bloodstains on the ground.

These scattered bloodstains stretched from where the victim's body lay, extending into the distance all the way to the toilet stall where the killer discarded the knife.

Clearly, just as Kudo Shinichi had deduced, these were bloodstains that dripped while the killer was carrying the knife to the toilet stall after committing the murder.

But Lin Xinyi saw more in these small bloodstains:

"This type of bloodstain, in forensics, is called a Drip Stain Bloodstain."

"A Drip Stain Bloodstain is formed when blood, under the influence of gravity, drips onto a surface."

"Generally, these bloodstains are circular or nearly circular."

"However, in most cases, the surface where the blood has dripped isn't smooth."

"Therefore, 'spines' will appear around the edges of the drip stain."

(They look something like this:)

As he spoke, Lin Xinyi motioned for Kudo Shinichi and Sonoko to come closer. He then crouched down, observing the small blood drops on the floor up close.

Sure enough, they both noticed that around the circular blood drops, there were visible "fine blood needles" radiating outwards in all directions.

At this point, Lin Xinyi further added:

"Look closely again. Are the spines on these blood drops mostly long on one side and short on the other?"

"They really are! Although it's not very obvious, you can still see that the spines on the left and right sides of a blood drop aren't the same length."

Miss Suzuki Sonoko exclaimed as if she had discovered a new continent:

"Why is that?"

"Because these blood drops were all shed while the culprit was in motion."

Lin Xinyi explained carefully:

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

"But at that time, the culprit was walking towards the toilet stall, so the blood drops falling from him would have a horizontal velocity."

"When these blood drops hit the ground, the blood will coalesce more in the direction of the velocity, and the spines in that direction will be longer."

"In other words..."

Lin Xinyi paused, then emphasized:

"The side with the longer spines indicates the culprit's direction of movement at that time."

"For example, if the long spines of this blood drop point towards the toilet stall, it proves that the culprit was indeed carrying the blood-stained knife and walking towards the toilet stall at that time."

"This..." Suzuki Sonoko was a bit confused:

"What's the use of knowing this?"

"The culprit went to the toilet stall to discard the weapon and gloves after killing someone, wasn't that Kudo Shinichi's conclusion already?"

"No, this is very useful."

It was Kudo Shinichi who spoke up in denial.

He stared intently at the ground, his gaze incredibly focused:

"I understand what Mr. Lin Xinyi means."

"The direction of the long spines on the blood drops can show the culprit's direction of movement at that time."

"And here, not all the blood drops..."

Kudo Shinichi pointed at a specific blood drop on the ground:

"...have their long spines pointing towards that toilet stall."

"Several of these blood drops have their long edge spines pointing in the exact opposite direction of the other blood drops!"

"Huh?" Suzuki Sonoko couldn't keep up anymore.

"Remember, the direction of the long spines on a blood drop indicates the culprit's direction of movement at that time."

Seeing Miss Sonoko looking a bit disoriented, Lin Xinyi re-emphasized this point of knowledge:

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

"These blood drops are different from the others; they didn't fall while the culprit was going to the toilet stall."

"They fell while the culprit was leaving this toilet stall and returning to the sink along the same path. That's why the direction of the long spines is completely opposite to the other blood drops."

"In other words..."

"After the culprit discarded the weapon in the stall and threw the gloves into the toilet..."

"Blood was still dripping from him!"

"The blood dripping at this point wasn't on the gloves and weapon; it was directly on the culprit's body."

Finally, Lin Xinyi earnestly summarized:

"So, it's not hard to imagine that the gloves didn't completely block the victim's gushing blood at the time."

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

"That's true..."

"However..."

Kudo Shinichi quickly found a flaw in Lin Xinyi's idea:

"That guy should have also gone to the sink to wash his arm after discarding the weapon and gloves."

"Otherwise, if his arm had noticeable bloodstains, it would have been difficult for him to blend into the crowd."

"That doesn't matter."

Lin Xinyi smiled very calmly:

"Even if he washed his hands thoroughly, it wouldn't make a difference."

"As long as he truly had blood on him, I'll definitely be able to expose him!"