"Calculate the angle of injection?"

Asai Narumi and Mao Liran glanced at each other, looking a little confused.

They weren't wondering how to calculate the angle of injection, but they were wondering:

"Does this still need to be calculated?"

"The gunshot wound on the deceased's head was a penetrating wound with two bullet holes at the entrance and exit of the shot."

"As long as the inlet and outlet are connected, can't you determine the trajectory of the bullet and the angle at which the bullet enters?"

Two points confirm a straight line, which is a very simple truth.

Since the trajectory of the bullet as it passes through the human body can be confirmed, the angle of the bullet can be estimated by simply measuring the angle between this straight line and the surface of the human body.

With this in mind, while raising doubts in their hearts, they unconsciously approached the corpse and observed the wound on the corpse's head:

"The bullet hole in the forehead is the entrance of the shot."

"The bullet hole in the back of the head is the shot out."

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

Before estimating the angle of entry, Moriran and Asai asked Lin Shinichi with some uncertainty.

One of them is a beginner apprentice, and the other is a forensic doctor who has just changed careers, and they are not good at examining injuries, especially gunshot wounds that are rarely encountered in ordinary times.

Now it is possible to determine the entrance and exit of the shot, mainly based on the splattered blood stains on the glass window behind the deceased, and indirectly confirm it through the spatial restoration of the imagination.

"Hmm." Lin Xin nodded and affirmed from the perspective of the characteristics of the wound:

"The inlet is a wound formed by a bullet striking, squeezing, and shearing the skin, which is generally similar to or slightly smaller in diameter than the warhead, and is accompanied by a skin defect in the center of the wound, and the edge of the defect shows skin involution, making the whole wound resemble a whirlpool funnel."

"The ejection port is a wound caused by the warhead penetrating the skin tissue, and the diameter of the ejection port is generally larger than the injection inlet, and it is accompanied by a tear in the wound skin."

"The traumatic characteristics of the two are still relatively easy to distinguish, and there is no mistake about them."

He replied in the affirmative.

Then, without waiting for Mao Lilan and Asai Narumi to continue to ask, Lin Shinichi said:

"I know what you mean."

"The light is seen from the position of the inlet and the outlet:"

"The injection port on the forehead is only slightly higher than the injection port at the back of the head."

"If you simply connect two points into a straight line, you can confirm the 'Genesis' and estimate the injection angle... Hmm..."

Lin Xinyi didn't measure it, but through visual inspection, he casually estimated:

"It's about 7 or 80 degrees, which is a blunt angle."

"That's right."

Asai nodded and said what he thought:

"Since the bullet is fired from high to low, at a blunt angle, into the brain of the deceased."

"As long as the murderer is tall enough and holds the gun a little higher, higher than the head of the deceased, such a wound can be formed."

As he spoke, Asai Narumi also simulated the appearance of the victim according to his imagination.

He pretended to be forced to the wall by the murderer, and bent his knees slightly against the wall, so that his height was appropriately lowered.

And Mao Lilan, who stepped on a pair of high heels and had a higher height advantage, walked in front of Asai tacitly and cooperated to play the role of the murderer.

She held up a non-existent "pistol" in the air, condescendingly, and aimed the "muzzle" at Asai Narumi's forehead.

"Smack~!"

Mao Lilan acted devotedly, and even unconsciously dubbed the voice.

And after "killing Asai with one shot", she turned her head and said to Lin Xinyi:

"Mr. Lin, look..."

"My gun is just a little higher than Dr. Asai's head."

"When the gun is fired, the bullet shoots from high to low, and it naturally forms a blunt angle of penetration similar to that on the head of the deceased."

"In that case..."

"The murderer's shooting posture isn't that strange, is it?"

She said with some concern that she had doubts in her heart.

But Lin Xinyi shook his head gently:

"No, you're mistaken."

"You make this judgment based on the fact that the angle of injection is blunt."

"And you determined that the angle of penetration was blunt, and you simply connected the injection entrance and the shooting exit into two points, and estimated the angle between the bullet wound and the human body surface."

"This..."Mao Lilan was slightly stunned: "Mr. Lin, what do you mean..."

"Is it wrong to confirm the injection angle just by the position of the injection inlet and the shooting outlet?"

"No, that's true most of the time."

"After all, two points confirm a straight line, and this is true."

"But we have to analyze the problem on a case-by-case basis."

Lin Xinyi paused slightly, and explained carefully:

And now the question is: "

"The wounds formed by the bullet after entering the human body are sometimes not a straight line."

"First of all, as the range of the warhead increases, the flight attitude also becomes less stable."

"Secondly, when the warhead hits the human body, it encounters resistance and sometimes changes the direction of its operation."

"Especially in this case... The deceased was hit by the frontal bone, which is almost the hardest bone in the human body. ”

"Therefore, the wound formed by the bullet passing through the human body is not necessarily a straight line, and curves, or even broken lines, may occur."

"This can have a big impact on the judgment of the angle of the shot."

"In particular, judging only based on the straight connection of the entrance and exit is prone to great deviations."

He explained carefully, so that Maoliran and Asai Narumi both reacted:

"I see..."

"Since the creation of the road may not be a straight line, the method of confirming the straight line with two points and then estimating the angle of injection cannot be applied here."

"Well, in this case... How do you determine the angle of injection? ”

Both blinked their big watery eyes, their eyes full of curiosity.

And Lin Xinyi continued to explain:

"It's simple, I said it before..."

"If the warhead is fired into the human body at an angle, an oval-shaped skin defect will form in the mouth."

"The sharper the angle of injection, the more 'flattened' the oval-like shape formed."

"I just saw that the shape of the skin defect at the injection entrance was too 'oval', so I felt that there was a problem with the injection angle."

"And it's very easy to calculate the angle."

"Measure the length X of the long axis and the length of the short axis Y of that oval wound."

"Then Sinα = Y/X, α is the angle of injection."

This is a sinusoidal inference algorithm that uses the difference in the diameter of the injection port and the relationship between the hit angle, and anyone who has studied junior high school mathematics can understand it.

Moriran and Asai Narumi quickly understood this method, and as Lin Shinichi instructed, they carefully measured the long and minor axes of the injection port with a ruler.

Through calculations, it was found that it was different from the original estimate of 7 and 80 degrees...

"The angle of penetration is only about 45 degrees."

"Shoot from high to low, and at a 45-degree angle to the surface of the human body..."

Narumi Asai imagined it a little:

"Did the killer raise the gun high above his head and then shoot down?"

"Or is it to jump up before the shot is fired and then shoot down?"

He imagined several of the killer's shooting stances, and the images he thought of were no different from performing acrobatics.

It was Mao Lilan who thought of a more reliable reason:

"Could it be that the deceased lowered his head or crouched down when he was shot?"

"It's also unlikely." Lin Xinyi shook his head:

"Because the bullet pierced the back of the head and then quickly chiseled through the glass window."

"The bullet as a whole is fired from high to low, which can be determined by the location of the exit and entrance."

"In this case, the height of the bullet hole in the shot exit must be higher than the height of the bullet hole in the glass window."

"And I measured it with a tape measure when I was doing the autopsy..."

"The height of the bullet holes in the glass window is only a few centimeters lower than the height of the deceased."

"If he crouches down again, or even lowers his head a little, the bullet will not be able to reach that height on the glass window after it cuts through his brain."

"Therefore, when the deceased was shot, he could only stand straight in front of the glass window."

Hearing this, Maolilan couldn't help but fall into deep thought.

She carefully observed the bullet hole in the glass window, and in her mind simulated the strange image of a bullet shooting into the forehead at a 45-degree angle, gouging through the deceased's head, and piercing the glass backwards.

The more I think about this picture, the more awkward it becomes.

If the deceased was standing straight in front of the glass window like this, then the murderer would have to fly to the ceiling and shoot at this angle of infiltration.

"Wait..."

Mao Lilan's tightly furrowed brows suddenly relaxed:

"We've been using this glass window with a splattered blood stain as a reference to guess where the deceased stood."

"Because the glass window is now closed vertically, Mr. Lin, you speculate that the deceased must have been standing straight in front of the glass window at that time."

"But... This glass window wasn't necessarily closed at the time! ”

"After all, the deceased collapsed on the window when he died—the window that was originally open is likely to close itself as the body slides down against the window."

Maorilan muttered as she looked at the tightly closed glass window.

"It doesn't have to be closed..."

Lin Xinyi suddenly realized something:

This window is not an ordinary left-right sliding glass window, but a relatively rare, up-and-down opening and closing glass window.

As soon as it is opened, the angle between the glass plane and the ground will be tilted.

Thinking of this, he tried to push the upside-down opening and closing glass window outward.

The glass window tilts and flips, with the top half facing outwards and the lower half facing inwards.

"Could it be...."

"The scene we just imagined was all wrong?"

Under Mao Lilan's reminder, Lin Xinyi found a completely different direction of analysis.

He poked his head out of the open glass window, and his head naturally looked up:

"This shot wasn't fired in this room at all."

"Rather, it was fired from upstairs, vertically downwards."