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

In the cold air of the autopsy room, assistant Xiao Li stared at the gray-white maggots wriggling in the tray, frowning and unable to help but step back. Zhang Kai noticed his reaction, took off his goggles, pointed at the wriggling larvae and said, "Don't underestimate these uncomfortable little guys, they are important helpers for us to infer the time of death."

Zhang Kai picked up a pair of tweezers, picked up a large maggot, and placed it on a glass slide. He explained while operating a microscope: "During the decomposition process of a corpse, the activities of insects have a strict time sequence. Especially the calliphoridae insects, they have a strong tendency to gravitate to fresh corpses, and usually fly to the corpse to lay eggs within minutes to hours after death." He projected the image from the microscope onto a display screen nearby, and the black mouth hooks on the head of the maggot were clearly visible. "You see, these blowfly eggs hatch into first-instar larvae after 8-24 hours. They feed on corpse tissue and grow very fast."

"Then how do we use them to determine the time of death?" Xiao Li moved closer to the display screen, his eyes full of curiosity.

Zhang Kai pulled up a timeline of insect development: "The growth and development of insects are greatly affected by temperature, and we can use the law of accumulated temperature to calculate it. Simply put, the total amount of heat required for each generation of insects to develop from eggs to adults is regarded as a constant." He pointed to the curve on the chart, "For example, for blowflies, in an environment of 25℃, it takes 8-12 hours for eggs to develop into first-instar larvae, 24-36 hours to develop into second-instar larvae, and 48-72 hours to develop into third-instar larvae. We measure the body length of these larvae, observe their molting, and combine it with the recent local meteorological temperature records to roughly calculate their growth time, and thus infer the time of death of the deceased."

He picked up another slide, on which were several maggots that had begun to pupate. "Look at these pupae. The outer shell is dark brown. This is the pupal shell formed after the third-instar larvae molt. When the maggots develop to the end of the third instar, they will stop eating and look for a dry, hidden place to pupate. The length of the pupal period is also related to the temperature. At the right temperature, after 5-7 days, the adult will break out of the pupa."

"But if there is a change in the weather, such as a sudden drop in temperature, will it affect the accuracy of the judgment?" Xiao Li asked.

"Good question!" Zhang Kai nodded approvingly. "So we can't just rely on maggots as an indicator. In actual work, we will make a comprehensive judgment based on the corpse's livor mortis, rigor mortis, degree of decay, and the temperature, humidity, ventilation conditions and other factors of the on-site environment. In addition, different types of insects appear on the corpse at different times and in different orders. For example, after green flies, flesh flies and burying beetles usually appear. Their appearance time and number changes can provide us with clues."

Zhang Kai put down the tweezers and said seriously: "Insects are like the 'time recorders' of corpses. Their growth and development process is the time code written by nature on the corpses. As long as we master these codes, we can make the dead 'speak' and tell us the time they were killed."

Xiao Li nodded thoughtfully, and when he looked at the maggots in the tray again, his eyes were less fearful and more determined to find the truth. In criminal investigation work, every seemingly tiny detail may become the key to solving the mystery, and these maggots that people avoid are contributing to the pursuit of justice in their unique way.

He first used a ruler to measure the degree of rigor mortis: "All major joints in the body have been relieved, and the right mandibular joint can move at an angle of about 45 degrees, which is consistent with the characteristics of more than 72 hours after death."

The deceased's right index finger was picked up with tweezers, and the light blue fibers in the nail crevices were observed under a microscope: "It is preliminarily judged to be made of nylon, with a diameter of 15-20 microns, and obvious signs of tearing and breaking." A gas chromatography-mass spectrometer was then used to analyze the fiber's composition. The rapidly jumping peak curve on the instrument screen showed that the fiber contained dioctyl phthalate plasticizer, which is commonly found in agricultural tarpaulins.

The scalpel cut open the chest and abdomen along the midline of the corpse, and the corrupt gas suddenly released, forming a light green air wave visible to the naked eye. "The third and fourth ribs on the right side of the deceased were freshly fractured, and the fracture line was oblique and sawtooth, which was consistent with the characteristics of 6-8kg blunt external force." Zhang Kai used a bone saw to remove the broken bones and observed the fracture morphology of the trabeculae under a stereo microscope. "A large amount of hemorrhagic tissue was seen at the fracture end, indicating that the fracture occurred at the near-death stage."

When the pericardium was opened, tiny bubbles floated in the coagulated blood. "Sporadic bleeding can be seen on the surface of the heart, and there is a transverse tear at the root of the aorta." He lifted the torn tissue with a vascular clamp. "This kind of injury is usually caused by severe concussion, which may be the impact effect of the head being hit."

The real cause of death was revealed after the trachea was opened. Zhang Kai used tissue scissors to cut open the trachea longitudinally, and the swollen mucosa appeared dark purple: "The epiglottis cartilage was bleeding in flakes, and obvious indentations were seen around the glottis fissure, which was consistent with the characteristics of mechanical asphyxiation." He cut the tracheal tissue and put it into formaldehyde fixative. "We need to do tissue sections to observe the submucosal bleeding and confirm whether it was strangulation or rope strangulation."

The work of determining age adopts a multi-index comprehensive analysis method. The first is the morphological observation of the pubic symphysis. Zhang Kai placed the pubic bone under a stereo microscope: "The ossified tubercles of the symphysis have completely fused, the dorsal bone ridge has been absorbed significantly, and a bone bridge has appeared at the junction of the pubic tubercle and the pubic body, which meets the characteristics of stage III in the "Chinese Bone Age Determination Standard", corresponding to an age range of 35-40 years old."

Next was the tooth wear test. He removed the mandible of the deceased and used a microhardness tester to measure the thickness of the tooth enamel: "The wear of the central incisor reached level III, and the exposed dentin area was about 25%. Combined with the secondary dentin deposition rate of the teeth, the age should be 38-42 years old." Finally, the trabecular structure of the pubic ramus was tested by X-ray bone densitometer, and the ratio of cortical bone to bone marrow cavity data finally locked the age of the deceased at 39±1 years old.

When examining the digestive system, Zhang Kai discovered something abnormal. Only a small amount of paste-like substance remained in the deceased's stomach, which was confirmed to be pasta by amylase testing: "The stomach contents were emptied by about 80%, and combined with the degree of chyme advancement in the small intestine, the last meal should have been 6-8 hours before death." But more noteworthy were the diffuse nodules on the surface of the liver, "which were consistent with the pathological changes of mild liver cirrhosis, and a liver puncture biopsy was needed to confirm the cause."

Seven hours into the autopsy, Zhang Kai began to examine the old injuries on the body surface of the deceased. On the left waist, he found an irregular scar measuring 7×12cm, and then Zhang Kai began to observe it using a dermatoscope. (End of this chapter)