Attending ex-girlfriend's wedding, arresting the groom's officer on the spot

"Send it for testing immediately for DNA typing and trace evidence analysis." Yang Sen packaged the sample into an anti-contamination evidence bag and marked the latitude and longitude coordinates and altitude accurately on the label.

When the multi-band light source switched to 450nm blue light, a lavender fluorescent reaction suddenly appeared on the west side of the well wall. Yang Sen quickly put on an orange filter and used a handheld exploration light to illuminate at a grazing angle - that was the unique Luminol luminescence pattern of splashing blood. "Take a photo to record the parabolic angle of the blood drop," he measured the vertical distance of the farthest blood spot from the ground, which was 1.2 meters, "combined with the height of the deceased, this means that this is not the first scene."

The portable X-ray fluorescence spectrometer beeps, and abnormal lead content is detected in the soil on the well wall. "This lead content is three times higher than the national standard," Yang Lin compares it with the database, "and it is highly consistent with the soil composition of the battery factory that was demolished three months ago." He uses a geological hammer to collect surface soil samples, and each sample is packaged in layers according to depth, with labels indicating the sampling azimuth.

The inspection of the deceased's clothing reached a deadlock. The faded overalls had been vacuum metallized, but still showed no fingerprints or palm prints. Yang Sen laid the pants flat on an anti-static table and scanned them inch by inch with a stereo microscope. The cement debris attached to the trouser legs revealed clues under the electron probe - the silicon dioxide content was 92%, and the calcium oxide content was 7.8%, which matched the PO 42.5 cement composition used in the construction site in the west of the city.

When the 0.1D scan was completed, the point cloud data had constructed a well bottom model accurate to 45 mm. Yang Sen virtually reconstructed the deceased into the scene and inferred the falling posture through the skeletal joint angles: "The hip joint was abducted 120 degrees and the knee joint was flexed degrees, which is consistent with the characteristics of active falling into the well. However, combined with the strangulation marks on the neck," he called up the CT D reconstruction of the rope groove, "the deceased should have been strangled and then thrown away."

As dusk fell into the wellhead, the evidence bags at the scene were neatly arranged in a matrix. The labels numbered GX-2024-0927-01 to 37 glowed in the sunset. From the hemp rope fibers to the moss on the well wall, each piece of evidence had undergone a complete packaging chain record. Yang Sen used a laser rangefinder to calibrate the well depth for the last time - 7.32 meters. This number will become a key parameter in calculating the impact force of the fall in the autopsy report.

By the evening, the body had been transported back to the Criminal Investigation Brigade, where forensic doctor Zhang Kai began to perform an autopsy.

The stainless steel door of the autopsy room slowly slid open, and the cold air with the pungent smell of formalin hit him in the face. Zhang Kai straightened his white coat and glanced at the electronic clock on the wall - 3:17 in the morning, the dark blue numbers jumped in the dark. Assistant Xiao Chen had already moved the body out of the refrigerator, and the condensed water on the surface of the body bag slid down the zipper gap and formed a small puddle on the ground.

"Let's get started." Zhang Kai put on an N95 mask and wrapped his hands in three layers of latex gloves. The moment his fingertips touched the stainless steel scalpel, the unique coolness of the metal spread along his palms. When the zipper of the body bag was completely unzipped, a foul smell mixed with rotten meat and cadaverine surged out. Xiao Chen subconsciously took a half step back, and his Adam's apple rolled violently. The deceased remained in the curled-up position when he was found, with dark purple corpse spots on his skin and a dark brown groove on his neck like an ugly centipede, running diagonally from below the left ear to the right clavicle.

"Body length measurement." Zhang Kai picked up the electronic ruler, and the red laser beam swept from the top of the head to the heels. The LCD screen showed 172.3 cm. He wrote quickly in the notebook, and the tip of the pen made a rustling sound as it moved across the paper. "Weight 68.7 kg, BMI index 23.1, muscle content is lower than normal, and it is estimated that daily physical activity is less." When the scalpel cut open the clothes of the deceased, there was a slight tearing sound at the adhesion between the fabric fibers and the skin, and half a crumpled lottery ticket fell out of the pocket of the faded overalls, with dark red stains on the corners.

Determining the time of death is the primary task. Zhang Kai slowly inserted the rectal thermometer into the body. The coolness from the metal probe made him frown slightly: "Rectal temperature is 24℃, and the current room temperature is 18℃." He checked the formula table and tapped quickly on the calculator with his fingertips, "According to the cooling rate of 0.83℃ per hour, the time of death was about 36-40 hours ago." But this result still needs to be verified. He turned to the operating table and used a sharp scalpel to cut open the eyelids of the deceased. The transparent vitreous humor was carefully extracted into a test tube. "For the potassium ion concentration test, remember to mark the sampling time." He handed the test tube to Xiao Chen, "The potassium ion concentration in the vitreous humor is the 'golden evidence' of the time of death."

Age inference is like a jigsaw puzzle, which requires a multi-dimensional chain of evidence. Zhang Kai first measured the length of the deceased's humerus with a vernier caliper. The metal caliper made a crisp "click" sound when it closed: "32.6 cm, combined with the formula, the age is between 30 and 45 years old." But this is just a rough estimate. He then picked up a magnifying glass and carefully observed the fine structure of the pubic symphysis. The ceiling light in the dissection room cast light and dark shadows on the surface of the bones. He whispered his observations: "The symphysis surface is nodular, the ossification center is basically fused, but the ridge groove is still clearly visible, which meets the characteristics of 35-40 years old in the "Chinese Bone Age Determination Standards."

The world under the microscope reveals more secrets. Zhang Kai cut a bone tissue sample from the rib of the deceased, and after twelve processes including decalcification, slicing, and staining, it finally presented a microscopic picture on the slide. Under the polarized light microscope, the changes in the Haversian system were clearly visible: the number of bone units decreased by 30%, the diameter increased to 150 microns, and the trabeculae were fractured and reconstructed. He operated the image analysis software and compared the data with the database. The age prediction range that popped up on the screen was 38-42 years old. "Bones are like the diary of life," he said to the recorder, "Every fracture and every metabolism leaves a mark on it."

Teeth provide another important dimension. Zhang Kai turned on the dental mirror, and the cool white light illuminated the inside of the mouth. The caries on the left second molar of the mandible reached deep into the pulp cavity, and the traces of root canal treatment on the right maxillary first molar were clearly visible. He called up the national dental treatment database and entered the production batch number of the treatment material: "3M's resin material produced in the third quarter of 2021. This model is only used in seven clinics in this city." When he measured the degree of tooth wear, he found that the enamel had disappeared over a large area, and the dentin was exposed to form a smooth plane: "This wear pattern usually occurs in people who chew betel nuts for a long time or work in occupations that require frequent biting."

In order to obtain the most accurate age data, Zhang Kai decided to use radiocarbon dating technology. He selected the collagen in the femur of the deceased. Once formed, this protein no longer participates in human metabolism, and it seals the carbon isotope information like a time capsule. The mass spectrometer in the laboratory made a low hum, and soon, the results came out. (End of this chapter)