Chapter 260 Technical Analysis
From a professional perspective, footprint identification analysis mainly focuses on three elements.
The trace body is the subject that makes the footprints, barefoot, shoed foot or socked foot.
The mark-bearing body is the ground or other objects that bear footprints.
The third important factor is the force. In addition to the gravity of the human body, there is also the muscle contraction force of the soles of the feet.
In the vast majority of cases, the type of footprints encountered are shoe prints.
It is rare for a suspect to walk around a crime scene without shoes, barefoot or wearing only socks.
The footprint identification that Lu Chuan came across were all shoe prints.
Compared with barefoot prints and socks-wearing prints, this type of footprint has a distinctive feature. The shape of the shoe print is strictly limited by the shape of the shoe.
For example, feet of size 41 can wear shoes of size 40, and even shoes of size 42 or even size 43.
This brings a lot of uncertainty to the footprint identification analysis.
Therefore, the size and length of the footprints are confusing in the footprint identification analysis.
General spot surveys, based on the fixed formula of foot length and height, will inevitably have errors.
Although Lu Chuan has not yet been to the scene to see the footprints, nor has he seen the footprint model, but just from the photos, he knows that the current investigation by the Criminal Police Brigade of the High Speed Rail New District has judged the height of the suspect. , there should be a problem.
Lu Chuan first analyzed the measurement data of the shoe prints.
Comparing the total length of the foot, the width of the arch, the width of the sole of the foot, and the width of the heel can roughly determine the height and weight of the footprint owner.
But it is only a range.
It depends on the depth of the footprints left on the ground.
This requires experiments to verify and compare the weight of the owner of the shoe print.
This is actually the simplest.
People of different weights leave different footprints on the same ground.
As long as you find a person with a known weight, step on a new footprint where the suspect left a shoe print, and compare the depth of the two footprints, you can calculate the suspect's weight.
Of course, now because Lu Chuan only saw the photos, he couldn't make these measurements.
Only the basic situation can be analyzed.
The high-speed rail new area criminal police brigade conducted an on-site investigation and collected twelve sets of footprints at the scene.
There are so many footprints, and among them are the footprints left by the suspect during his continuous march.
In this way, Lu Chuan can analyze the characteristics of the footwork.
The first is the stride feature.
Be able to determine the step length, step angle and step width of the suspect's walking.
But generally speaking, determining the stride characteristics cannot be accomplished by just one or two footprints.
It takes at least four consecutive steps forward to make this analysis.
With continuous footprints, it is relatively easy to measure.
"Step length...forty-five centimeters."
Generally speaking, an adult male with a height of 1.7 to 1.8 meters has a step length of 50 centimeters to 80 centimeters. cm.
Of course, there are also requirements for the current survey measurement step length.
The distance from the toe of the back foot to the heel of the front foot, not including the length of the feet, is the stride length.
However, the suspect's step length was only forty-five centimeters.
This data can be said to be significantly lower than the average step length of adult men.
According to current surveys, there are three standards for judging step length. Generally speaking, if it exceeds 80 centimeters, it is a long step, and if it is 71 to 80 centimeters, it is called a medium step.
Anything less than seventy centimeters is a short step.
The suspect's step length is the shortest of short steps.
However, combined with Lu Chuan’s inference about the suspect’s height just now, it is reasonable.
"Step angle...outward 7.2 degrees"
Most people's step angle is around 6 degrees, close to 7 degrees. The suspect has a slight outward splay.
"Step width...8.1 cm, normal."
The measurement analysis of step width is actually more complicated than step length and step angle.
Every person’s step length and step angle are not unique. It's very easy to find two people with the same step length.
The same is true for the step angle. For most people who walk normally, the step angle is basically around 6.7 degrees.
Even if there is a slight difference, it is not particularly big.
But the step width is different.
In reality, it is rare to find people with exactly the same step width.
The current survey divides step width into many categories.
For example, separated steps, combined steps, combined steps, straight steps, staggered steps, etc.
The suspect's step width is within the range of most normal people.
The last thing Lu Chuan did was analyze the suspect's gait characteristics.
Different people have different gait characteristics.
For example, when some people walk, their heels touch the ground first, while others touch the soles of their feet first.
This is the characteristic of settling down.
Kick-off also has characteristics. Some people push their feet hard when they kick-off, some people push their heels, and some people push their toes.
In this case, every footprint is actually dynamic.
Based on the different pressure changes in the front, middle and back of the footprints, many characteristic information of the suspect's walking can be determined.
For example, the pedal mark at the start is reflected in the footprint as the deep mark of the forefoot. If it is on the dirt ground, the soil will move backward.
Another example is the scratch marks when starting. The toes are pressed down, creating a crescent-shaped depression.
Lu Chuan's identification and analysis was very careful. More than an hour has passed and it has not been completed yet.
Liu Guodong and others did not bother.
Similar to identifying and analyzing fingerprints, this kind of work requires calmness and concentration.
Of course, compared with the identification and analysis of fingerprints, the identification of footprints requires a lot of precise measurements and data calculations.
Based on Lu Chuan’s work experience, doing footprint identification analysis is more tiring than doing fingerprint identification analysis.
“Huh…”
Two and a half hours later, when it was almost time to get off work, Lu Chuan finally took a long breath.
“Done?”
Lao Bai brought over a cup of tea. Lu Chuan took it and drank it.
“It’s almost done, but we still have to go to the site to see, otherwise some data may not be accurate.”
Lu Chuan looked at Liu Guodong.
The other party nodded: "I just called and asked. The scene is still there. You should be able to go and have a look."
"Are you going now?"
Lao Bai looked at the sky and then It will be dark after a while.
"Go, the night is long and the dreams are many."
"Okay, I'll go with you. Lao Yang wants to go home to be with his son, and I have nothing to do."
"Master, let's set off then."
"Okay, I'll contact the high-speed rail new area, and Zhang Qi will send someone to cooperate with you."
An hour later.
Baomidi, Xitou, Xitou, Xinjian Village, High-speed Railway New Area.
In Haizhou at the end of April, the corn seedlings had just grown and were no taller than chopsticks.
But it’s lush and green, and the air is fresh.
"Teacher Lu, this is the crime scene."
The person coming from the High-Speed Railway New Area is none other than the investigator who collected the footprints, Sun Miao.
The two knew each other and participated in the city bureau’s fingerprint competition together at the beginning of the year.
It’s just that Sun Miao used to call Lu Chuan Lu Chuan, but now he calls him Teacher Lu.
(End of this chapter)