eurekapd Chapter 1041 In-depth On-site Investigation and Analysis
Chapter 1041 In-depth On-site Investigation and Analysis
The investigation at the bottom of the excavation pit proved even more challenging. Xiao Sun donned a gas mask and, holding a portable gas chromatograph, brought it close to the decomposing corpse: "Peaks in hydrogen sulfide and cadaverine were detected, consistent with late-stage decomposition." He carefully parted the corpse's curled fingers; between the fingers, besides soil, were embedded fibrous material—"grayish-white fibers, possibly fabric or rope," he said, immediately sending it for microscopic analysis." Xiao Yang, meanwhile, focused on the soil indentations beneath the corpse, using plaster casting to create a three-dimensional model: "The indentations were irregularly concave, indicating that the corpse had slid after being thrown."
As the investigation light swept across the victim's overalls pocket, Xiao Yang noticed a light brown stain on the inside of the fabric. "Luminol test." He sprayed the reagent; the stain instantly fluoresced a bluish-white, confirming it was blood. A sample was taken for ABO blood typing. Simultaneously, Xiao Sun extracted scrapings from under the victim's fingernails. The tissue picked up with tweezers contained fine wood shavings: "Wood species identification may reveal the environment of the crime scene."
Outside the excavation pit, the two men discovered suspicious shoe prints. However, frequent mechanical crushing at the demolition site had left only the edges of the prints. "It was made of rubber with a diamond-shaped grid pattern." Xiao Yang used a laser rangefinder to measure his stride: "78 centimeters long, 10-degree stride angle, estimating his height to be 175-180 centimeters, most likely male." Xiao Sun took out an electrostatic adsorption device to try and extract the potential shoe prints, but the instrument's display only showed chaotic interference patterns.
As the investigation deepened, more details were revealed: cement debris adhering to the soles of the deceased's shoes differed from the markings commonly used at construction sites; oil stains on the trouser legs, analyzed by thin-layer chromatography, contained cyclohexane; DNA extracted from saliva stains on cigarette butts scattered at the scene was unidentifiable due to severe decomposition. As the setting sun stained the investigation tent blood-red, Xiao Yang labeled the last piece of evidence: "All physical evidence at the scene has been numbered, totaling 32 items in 7 categories."
Xiao Sun shut down the 3D scanner and synchronized the data to the branch server: "Although there is no direct evidence pointing to the murderer, the cross-comparison of these microscopic pieces of evidence may be able to construct a complete reconstruction of the crime scene." The two took off their mud-covered protective suits, their gaze finally settling on the livid ground at the excavation pit—the undeciphered scratches, fibers, and bloodstains awaited the interpretation of the laboratory's sophisticated instruments, like silent witnesses waiting to be awakened.
The operating lights in the autopsy room shone brightly in the dead of night. Under the cold white light, forensic pathologist Zhang Lin, wearing a protective mask and double-layered latex gloves, pressed a scalpel against the swollen, decaying skin of the deceased. The body was dark green due to its advanced decomposition, its abdomen swollen like a ball, emitting a nauseating stench that almost penetrated the protective gear.
"The deceased was male, 176.5 centimeters tall." Zhang Lin began recording into his voice recorder, while simultaneously measuring precisely with a tape measure. "The livor mortis is fixed on the uncompressed area of the lower back, and is a dark purplish-red color; the cornea is highly cloudy, making it impossible to see the pupils; putrefied veins are present on the abdomen, and the subcutaneous tissue has a marble-like pattern." He opened the deceased's eyelids, and the pupils had already diffused into a hazy gray haze. "Based on the degree of decomposition of the body, combined with the recent average daily temperature of 28°C, the preliminary estimate of the time of death is 18-25 days ago, but further confirmation through entomological evidence is needed."
An assistant handed over a rectal thermometer, which read 24°C. Zhang Lin frowned as he checked the autopsy room's temperature control system: "The room temperature is 26°C. The body is buried underground, and the soil's thermal conductivity will affect the cooling rate." He flipped through his notebook, referring to the formula. "Based on an estimated 0.3-0.5°C drop per hour for a buried body, the corrected time of death should be 20-22 days ago." Suddenly, he noticed maggots crawling out of the deceased's nasal cavity and mouth. "Extracting blowfly larvae at different growth stages for age determination will allow for a more precise pinpoint of the time of death."
In the entomology lab next to the autopsy room, Zhang Lin carefully placed blowfly larvae extracted from the deceased's nasal cavity and oral cavity into a petri dish. These larvae, each with its own unique shape, wriggled slightly in the saline solution. Their transparent to off-white bodies had black mandibles that gleamed with an eerie luster, as if silently telling the secrets of the death scene.
“First, we need to identify the species of the larva,” Zhang Lin said to his assistant, picking up a stereomicroscope and adjusting the magnification to 40x. Under strong light, the morphology and structure of the larva's posterior spiracles were clearly visible. “This is a green bottle fly larva. Its spiracular plates are oval, with the spiracular knob located in the center of the spiracular plate. It has a three-lobed spiracular slit, which is a typical characteristic of this species.” After identifying the species, he selected 10 plump and active larvae from each of the three different growth stages of the larval population to prepare for age determination.
The first larva was in its early instar stage, as small as a grain of rice, with a soft and transparent body. Zhang Lin placed it on a glass slide, added a drop of lactic acid phenol staining solution, covered it with a coverslip, and observed it under a biological microscope. Under 400x magnification, the pharyngeal bone structure of the larva's head was clearly visible. "The pharyngeal bone of the early instar larva is slender, and the dorsal angle and ventral angle are almost equal in length, which is an important basis for judging that it is in the first instar stage." He measured the length of the pharyngeal bone to be 0.12 mm and recorded it in his experimental logbook.
Next, Zhang Lin selected a middle-instar larva. Compared to the early instar, this larva was significantly larger, and its body surface showed pale yellow pigmentation. Under a dissecting microscope, he carefully separated the larva's head and body using a microdissecting needle. "The pharyngeal bone of the middle-instar larva begins to thicken, and the length of the dorsal angle is about 1.5 times that of the ventral angle." He measured the length of the larva's pharyngeal bone to be 0.35 mm, and also observed that fine wrinkles began to appear at the edges of the spiracular fissures on the posterior spiracular plate of its abdomen. "These morphological changes are all signs of larval development."
Finally, there were the last instar larvae, which were robust in shape and light brown in color, showing signs of impending pupation. Zhang Lin immersed the last instar larvae in 60°C hot water for 3 minutes to soften their body tissues, making it easier to observe their internal structures. After the larvae cooled, he used a microsurgical knife to cut along the midline of the larvae's abdomen and removed the digestive tract for processing. Under the microscope, food residue in the digestive tract was clearly visible. "The digestive tract of the last instar larvae is usually filled with undigested food particles, and the Malpighian tubules in the midgut are darker in color. These characteristics indicate that it is in the final stage of larval development." The pharyngeal bone length was measured at 0.78 mm, far exceeding that of the previous two instars.
After completing the morphological observation, Zhang Lin began to use the developmental accumulated temperature method to calculate the larval growth time, and found that this time was about 21 days ago.
However, Zhang Lin did not rush to conclusions. He then tested the protein and hormone levels in the larvae.