Recently, the British "Nature·Communication" magazine published an article saying that European scientists based on biobank data analysis showed that changes in gene expression caused by death in different tissues can be used to estimate the death time of the deceased. The news has aroused widespread public concern.
In the field of criminal investigation, the determination of the time of death is one of the most important clues to solve the crime. The related research around it has not stopped. However, the reality is not as optimistic as we think. Experts say that the industry still uses traditional methods, and the gene expression determines the time of death. Although forensic experts have been studying for many years, they still stay in the laboratory, and there is still a long way to go before real applications.
There is no perfect way
So far, the technical means of inferring the time of death in the field of forensic science is mainly based on the phenomenon of corpses, such as corpse, corpse, corpse temperature, etc., the degree of digestion of the stomach content and the growth and changes of the plants around the body. "Accurately inferring the time of death is a recognized problem in the forensic science community. At present, there is no 'golden indicator' that is not affected by individual differences and post-mortem changes, which can be used in actual cases." He Guanglong, deputy director of the Forensic Pathology Damage Technology Department of the Ministry of Public Security .
From a professional point of view, the method of inferring the death time based on the corpse phenomenon is mostly related to statistics, and there are related formulas. However, it is said that the various factors such as the temperature and humidity of the environment, the physical condition of the deceased, and the cause of death all cause individual differences in post-mortem changes, thus affecting the accuracy of the inference of death time. For example, it is estimated that the early death time is widely used in the current case through the change of cadaver temperature, but the change of cadaver temperature is interfered by many factors such as the fat and thinness of the deceased, the state of clothing, and the temperature change of the surrounding environment. In the same environment, the corpse temperature of the fat man is slower than that of the thin body; the temperature of the corpse in the warm room is colder than that of the cold outside. Therefore, the identification of death time in forensic science is now a relatively rough time interval segment.
Why is "gene expression" not currently reliable?
About a decade ago, the Chinese forensic science community began to explore whether it is possible to obtain more accurate death time by monitoring changes in gene expression after death, including Liu Liang, a professor at Huaji University of Science and Technology, and his team. "Relationship between nuclear DNA degradation and death time in mouse skeletal muscle cells", "Using RNA degradation rules to construct mathematical models to infer death time", "Research on the relationship between DNA content and death time of human liver cells after death" and other research results are published in authoritative journals. .
However, most of these studies have been stagnant. Industry insiders told the Science and Technology Daily reporter that this research has not made much progress. Some key problems have never been broken. Old problems such as individual differences and realistic interference factors cannot be solved. More importantly, the results have never been able to move from the laboratory to the application.
Because the laboratory environment is stable and single, the real cases are very complicated, and every subtle difference will affect the identification. He Guanglong believes that the use of changes in gene expression after death to determine the time of death is far from the real application.
Chinese forensic experts are studying å•¥
In fact, both forensic scientists and biologists have been exploring ways to make death time more precise.
For example, in recent years, experts have found that the concentration of potassium and strontium ions in the body of the corpse is related to the time of death. Chinese experts have done a lot of research. Because vitreous humor is less affected by the outside world, it is rarely affected by pollution and spoilage, and the changes of various components are relatively stable, so the measured death time is relatively accurate. However, the academic community still has some controversy about the model and calculation method of this method.
Another method of concern to professionals is forensic entomology. In the American drama "Criminal Scene Investigation", it was the application of this method to judge the death time by insect behavior. However, because the flies of different species have different hatching, larval growth cycles and phlegm time, it is necessary to judge not only the type of flies on the corpses, but also the growth cycle of different flies, and different regions. Problems with different insect species and growth cycles.
He Guanglong said that innovation in the field of identification is the norm – both researching new methods and focusing on old method innovations. He is optimistic about the application prospects of forensic entomology, but if we want to promote this research, the forensic community has to work together with agronomists and entomologists. (Technology Daily)
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