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

"There were still small, unburned charcoal particles at the bronchial bifurcation, indicating that the deceased still had respiratory function during the cremation." Zhang Kai examined the sample under a microscope. The charcoal particles were evenly distributed on the surface of the tracheal mucosa, and the mucosal epithelium showed obvious thermal damage—the cells exhibited ballooning degeneration and nuclear pyknosis. "This is a typical heat-induced respiratory syndrome," he noted in the report. "Combined with the charcoal deposits in the lung tissue, we can preliminarily determine that the burning occurred before death, and the deceased still had vital activities during the fire."

But the determination of the cause of death took a turn. Zhang Kai's scalpel paused on the charred myocardial tissue; the charred heart resembled a burnt walnut, its surface covered with a layer of grayish-white ash. He gently brushed aside the charcoal debris from the right ventricular wall with a probe, and a 1×2cm hemorrhage suddenly appeared, the dark red spot resembling a congealed scab on the dark brown myocardium. "Xiao Lin, get the tissue forceps." His voice was muffled through his mask, and as the forceps picked up the tissue at the edge of the hemorrhage, charred fragments fell off in a rustling sound.

“The shape of this hemorrhage spot is very unusual,” Zhang Kai said, placing the tissue sample on a glass slide. “The edges are star-shaped, and there is a depression in the center, which does not resemble thermal injury caused by high temperature.” Xiao Lin’s microscope lens was aimed at the sample. The cell structure on the screen was already blurred, but the broken bands of myocardial fibers could still be seen: “Professor Zhang, the myocardial fibers here have wavy deformation and necrosis of the contractile bands—this is a typical feature of myocardial injury before death.”

As the scalpel cut open the left ventricle, a stream of dark red liquid suddenly gushed out, forming a small pool of blood in the tray. "The heart blood hasn't completely coagulated," Zhang Kai said, testing it with pH paper. The paper turned pale red. "The pH is 6.8, slightly acidic, which is consistent with the characteristics of blood in a hypoxic environment." He picked up a 10ml syringe, and as the needle pierced the ventricular cavity, the needle tip encountered slight resistance—although the myocardial tissue was carbonized, it still retained some elasticity.

The drawn blood was a cherry-red color in the syringe, like red wine mixed with rouge. "This color is so typical," Zhang Kai said, holding the syringe up to the light. "It's a characteristic change of elevated carboxyhemoglobin. Normal blood is dark red because it contains reduced hemoglobin, but when carboxyhemoglobin saturation exceeds 30%, it will appear this cherry-red." Xiao Lin had already prepared the test reagents, and when she dripped the blood onto the colorimetric plate, the reagents immediately turned purplish-red.

“Normal carboxyhemoglobin saturation is below 5%, and non-smokers are usually below 2%,” Zhang Kai said, looking at the color change on the color chart. After comparing it with the standard color scale, the value showed 35%. “This concentration is in the range of moderate poisoning, which can cause headaches, nausea, and confusion, but it has not yet reached the lethal concentration—usually it needs to exceed 50% to be fatal.” He suddenly remembered the ash in his trachea. “This means that he survived for a period of time after inhaling a large amount of carbon monoxide, and may even have struggled during the fire.”

Xiao Lin's finger traced across the test manual, then suddenly pointed to the "Carboxyhemoglobin Metabolic Rate" column: "Professor Zhang, based on a 15% metabolism per hour, a 35% saturation level means that before he stopped breathing, the actual carbon monoxide concentration he inhaled might have been as high as 50%, only some of it was metabolized during his survival." Zhang Kai nodded and marked the location of the hemorrhage on the anatomical diagram with a marker: "This explains the myocardial damage—severe hypoxia leads to metabolic disorders in myocardial cells, causing necrosis of the systolic bands."

He had Xiaolin take a blood sample for blood gas analysis. The results showed a blood oxygen partial pressure of 35 mmHg, a carbon dioxide partial pressure of 60 mmHg, and a bicarbonate concentration of 22 mmol/L. "Type II respiratory failure," Zhang Kai noted in the report, "hypoxia accompanied by carbon dioxide retention, consistent with the blood gas characteristics of carbon monoxide poisoning. However, a carboxyhemoglobin saturation of 35% is insufficient to explain such severe respiratory failure; there must be other reasons."

When the test results came out, Xiaolin suddenly exclaimed, "Oh dear!" "Teacher Zhang, the lactate dehydrogenase activity in his blood is three times the normal level!" she pointed to the numbers on the lab report. "The creatine kinase isoenzyme is also elevated, indicating severe damage to the myocardial cells, possibly caused by poisoning or hypoxia." Zhang Kai stared at the bleeding spot and suddenly realized something: "He was already in a state of severe hypoxia before he was burned. Carbon monoxide poisoning is only one factor; there are likely other toxins involved."

He re-examined the heart's blood vessels and found a carbonized thrombus at the entrance of the left circumflex coronary artery. "There's an embolism here!" Zhang Kai gently probed with a probe. The thrombus was hard and covered with a layer of grayish-white substance. "Although the structure has been damaged by the high temperature, it can be seen that it is a mixed thrombus with platelet and fibrin components—this was formed before death, not after death."

Xiao Lin suddenly remembered something and pulled out the lung tissue test report: "Teacher Zhang, the protein content in the edema fluid of the lung tissue is as high as 5g/L, which is three times higher than normal. This indicates acute pulmonary edema, further supporting the conclusion of hypoxic respiratory failure." Zhang Kai dripped cherry-red blood from the syringe onto filter paper. As the bloodstain spread on the paper, the edges showed varying shades of red: "A carboxyhemoglobin concentration of 35% is enough to render him unable to resist, but to kill him, a more lethal factor is needed—either continuous inhalation of carbon monoxide or other poisons."

He asked Xiaolin to prepare a quantitative test for carboxyhemoglobin while he began examining the other organs. When the scalpel cut open the liver, the cut surface was dark red, and the lobular structure was blurred, but fatty degeneration of the hepatocytes around the central vein was still visible. "The degree of fatty degeneration in the liver is mild," Zhang Kai noted, "which means that the hypoxia time is not too long, consistent with the poisoning duration corresponding to 35% carboxyhemoglobin—about 2-3 hours."

When the quantitative test results came out, Xiao Lin frowned: "The precise value is 34.7%, with an error of ±0.5%." Zhang Kai wrote out the formula on the calculation paper: "Based on a body surface area of ​​1.75㎡, the total amount of carbon monoxide he inhaled was about 2.3L. In a confined space, it would take burning at least 5kg of pine wood to produce that amount." He suddenly looked out the window, "But the mountain valley is an open environment, and carbon monoxide will spread rapidly. To reach this concentration, either the combustion would be extremely intense, or he would be confined to a closed space."

“This concentration is enough to cause impaired consciousness, but not fatal,” Zhang Kai circled the 34.7% value on the report, his pen drawing a heavy line on the paper. “This indicates that he survived for some time after inhaling a large amount of carbon monoxide. During this time, he may have suffered other injuries—such as that chest wound, or a more lethal toxin.” Xiao Lin had already begun preparing samples for the blood toxicology test; the centrifuge tubes spun rapidly in the centrifuge, humming loudly. (End of Chapter)