What is DNA Forensics?

A national judicial appraiser , in accordance with laws and regulations and industry operating standards, using various technologies or means, through public-to-public investigation, public-to-public evidence collection, on-site medical investigation, medical follow-up evidence collection, injury, etc. A set of legal medical appraisal conducted by the medical examination and observation of the living body, autopsy, symptom analysis, test comparison, observation and interrogation, identification of relics, monitoring and special examination. Eligible to assist the police in handling the case by investigating evidence is the core of public security organs' criminal investigation and investigation to obtain evidence and solve the case. Compared with clinicians who only focus on living medicine, modern Chinese forensics combines both " living medicine " and " death medicine " As research target. Forensic science is the scientific and technical personnel who use basic medicine, clinical medicine, and related criminal science technology and forensic appraisal technology to conduct investigation and identification of human bodies (living bodies, corpses, and spirits) and crime scenes related to the law and make identifications. The ancient forensic medicine is called Lingshi and zhuozhuo, mainly for simple autopsy examination (does not involve modern western medical science and technology, especially pathology ). In modern China, forensic science has become a complex open system, actively absorbing knowledge from mathematics, physics, chemistry, biology, psychology, and computer science and engineering, integrating modern science and technology systems into Dacheng, which is moving towards a The road of scientific, standardized, institutionalized, and standardized progress. Just as the legal system of the same country is divided into judicial power, legislative power, and executive power, correspondingly, forensic medical evaluation is gradually moving into three areas: judicial, legislative, and administrative. For forensic science, the human body (living body, corpse) is not the goal, the rule of law spirit and human rights awareness are the ultimate goals, and medical science is the means to achieve the goals.

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British geneticist Jeff reys first applied DNA fingerprinting to identify an immigration dispute in 1985. The creation of PCR technology in the same year opened the prelude to the rapid development of DNA analysis technology. With the continuous discovery of various new technologies derived from PCR and new DNA genetic markers, the DNA analysis technology is constantly updated.Some trace, corrupt, and even contaminated samples can be quickly identified, and the utilization rate of on-site biological evidence It has been greatly improved and has become a powerful weapon for identifying crimes. The forensic science DNA database perfectly combines the high individual specificity of DNA with the efficiency of computer information analysis, greatly expanding the scope of investigation, saving case handling resources, improving work efficiency, and fully showing the technical effectiveness of DNA. It embodies the powerful advantages of high-tech case resolution and has become the biggest breakthrough since the application of fingerprint technology in the 20th century.

1 The concept of a forensic DNA database

Forensic DNA database system, in a narrow sense, uses the organic combination of the high efficiency of various DNA analysis technologies such as STR-PCR and the high storage, efficient retrieval, and automation technology of computer technology. Human tissues, blood spots, fine spots, saliva spots, hair, bones, etc.) and blood spots or saliva spots of relevant persons (victims, suspects, etc.) were extracted, purified and quantified by DNA, and then passed through the STR locus After composite amplification and automatic DNA typing, the digital DNA typing results are obtained, and the data is imported into a computer with a statistical and comparison database system via the network to complete the automatic comparison of the DNA typing data in the library. A database system for matching or not DNA typing, drawing conclusions or excluding conclusions. The broad forensic science DNA database system should include DNA analysis data including the above functions and the standardized quality control system of the inspection technology, and biological samples (including blood samples such as former subjects, missing persons, paternity testers, etc.) for non-routine examinations of criminal cases. Processing system, network management system, and a series of complex and costly technical systems.

2 Composition of forensic DNA database

The forensic DNA database is composed of a criminal database, a former database, a DNA database on the scene of a criminal case, a database on the spot, and a basic DNA database.
2.1 Convicted offender DNA database
It is the application of DNA typing technology and computer storage and retrieval functions to blood samples of some criminal offenders. After DNA typing, the results are simplified into data, which are stored into the computer with other files for review and comparison when necessary for criminal investigation. To rule out criminal suspects or identify criminals.
2.2 Field Library (forensic casework sample DNA database)
It is the application of DNA typing technology and computer storage and retrieval functions. After the DNA typing, the results are simplified into data and stored in the computer for review and comparison when necessary for criminal investigation. The role of the case or excluding criminal suspects or identified criminals.
2.3 missing people DNA database
It is the application of DNA typing technology and computer storage and retrieval functions. The blood samples of parents of missing persons and blood samples of suspected missing persons (including trafficked children and unknown corpses) are subjected to DNA typing, and the results are simplified into data and stored in the computer. It can be used for criminal investigation to check and compare, so as to identify the source.
2.4 Basic DNA database
It mainly stores the chromosomal location of each locus, the gene frequency data and genotype data of related populations, related forensic application parameters such as heterozygosity (H), excluding probability of paternity (EPP), and personal identification rate ( probability of discrimination (Dp), polymorphism information contents (PIC), etc.

3 Structure and Duties of the Forensic DNA Database

3.1 The three-level structure of the national forensic DNA database <br /> are the central bank, provincial bank and municipal bank, respectively.
3.2 Duties 3.2.1 Central DNA Database a) Accept and manage DNA typing data and information codes entered by provincial DNA databases; b) Accept manual or automatic query comparison by provincial public security agencies, and manual query comparison by municipal public security agencies C) The case undertaken by the central authority as an independent unit, enters the DNA typing data and information code into the central DNA database according to the requirements of relevant standards.
3.2.2 Provincial DNA Database a) Accept and manage DNA typing data and information codes entered by municipal DNA databases; b) Regularly transmit DNA typing and information codes of the provincial DNA database to the central DNA database; c) Accept nationwide Inquiries and comparisons of local public security organs; d) According to the technical methods in GA / T383-2002, collect the DNA typing data of the local criminals and the DNA typing data of the biological evidence at the scene of the unbroken case, and enter the provincial DNA database. .
3.2.3 Municipal DNA Database a) Regularly transmit the DNA typing data and information codes of the municipal library to the provincial DNA database. B) Collect the DNA typing of local criminals according to the technical methods in GA / T383-2002 The data, as well as the DNA typing data of the biological evidence at the scene of the unsolved case, were entered into the municipal DNA database.

4 Functions of Forensic DNA Database

4.1 Querying criminal suspects < br Compare the DNA typing data of the biological evidence at the scene with the DNA typing data in the former library to find out the criminal suspect in a case. The on-site physical evidence DNA typing data is compared with the data in the personnel database. If the new data in the personnel database matches the on-site physical evidence database storage data (positive investigation), it can be prompted that the inventory case is done by the person. If the new data in the on-site physical evidence database matches the data stored in the personnel inventory (back-check), it can be prompted that the new case was committed by the former personnel. The comparison result is further determined by a review test. Realize the case to use the database to quickly find the case without the exact suspect.
4.2 Parallel Cases < br Compare the DNA typing data of the biological evidence on-site with the data in the physical evidence database. If a matching sample is found, the related case can be investigated in series. From 1999 to 2001, there were multiple rape cases in a certain place in Beijing. After examining the spot plaques in the scene, they entered the database and found that the DNA typing results were the same. They were done by the same suspect, and the cases were then investigated. During the storage period, blood samples of more than 10 criminal suspects were compared, and the results were all excluded. At the end of 2001, a blood sample of the suspect of the attempted theft was sent to the place for routine typing after DNA typing, and it was found that his typing was exactly the same as that of fine spot. Taking this as a breach, the offender explained the facts of more than 70 crimes.
4.3 Querying missing persons < br br Compare the DNA typing data of missing persons (unknown corpses or missing children) or the DNA typing data of their families (parents or spouses and children) with the missing persons' database, According to the genetic laws and DNA typing results, the kinship probability calculation can be used to find the corpse source for the unknown corpse, find the parents for the lost child, or find the lost child for the parent.

5 Construction of forensic DNA database

5.1 Construction of Foreign DNA Databases In 1994, the British formal legislation authorized the British Forensic Science Service (FSS) to establish a DNA database in the United Kingdom. In 1995, the world's first national DNA database was established in the UK. Subsequently, in some states in the United States, Canada, Australia, a few European, Asian, and African countries, the construction of national DNA databases has also begun. In 1997, the Canadian House of Representatives passed legislation authorizing the Royal Canadian Mounted Police to establish a DNA database. Austria and the Netherlands also started building warehouses in 1997. France, Portugal, Finland, and Norway started construction of DNA databases in 1998. In Asia, the Hong Kong Special Administrative Region of China passed legislation in 1999 to initiate database construction. In Africa, South Africa has also made some progress in database construction. At the International DNA Working Group seminar held by Interpol in France in 2002, a proposal was made to establish an international DNA database to improve the utilization of DNA information resources. As of July 2003, there were more than 1.7 million human samples in the UK's DNA database, and more than 150,000 on-site inspection samples. The on-site inspection ratio was 40% (matching with other sites or personnel), and the personnel database was on average. The rate reached 8%, with an average of more than a thousand cases solved every week. As of April 2003, the United States DNA Database Joint Search System (CODIS) has 1321854 personnel samples, 54895 on-site material samples, 778 cases compared with the average.
5.2 Construction of domestic forensic DNA database 5.2.1 Importance and necessity of establishing forensic DNA database The current DNA testing technology used in China is only a passive testing method, and technicians can only wait for the investigators to send them for inspection in the laboratory, and Materials and samples of suspects were compared to identify criminals. Establishing a DNA database can actively search for criminals, so as to give full play to the initiative in solving cases, provide clues for case detection, take the initiative to solve cases, and effectively save resources. The mobile crimes of the floating population and the repeated crimes of criminals with previous criminal records have increased the difficulty of solving the crimes and made the public security organs exhausted. The establishment of a national DNA database technically overcomes the regional limitations of investigating and solving cases. Through the DNA database network, cross-region crime cases are linked, which is conducive to consolidating cases and reducing the scope of investigation, so that cases can be resolved as soon as possible and prevent other victims. Further harm can also be a powerful blow to stray crime.
5.2.2 The establishment of a forensic DNA database is feasible In recent years, China's DNA testing technology has developed rapidly, and almost all provinces have DNA laboratories that can perform DNA testing. The DNA laboratories of the national public security system all have DNA typing data of many on-site inspection materials, and they have ready-made material conditions for establishing a DNA database. Shanghai, Beijing, Liaoning, Guangdong and other places have invested huge amounts of money to establish a forensic DNA database in this area and played a certain role in case detection. The comprehensive DNA database established by the Material Evidence Identification Center of the Ministry of Public Security has been networked with many provinces and cities through the public security private network to form a central database-provincial library-city-level database database model, which has enabled domestic inquiries. It won the first battle in the national special fight against abduction in 2000, and played an important role in the detection of many series of vicious cases. The exploration and practice of China's DNA database shows the feasibility of establishing a national forensic DNA database.
The Ministry of Public Security promulgated the "Forensic Science DNA Laboratory Test Specifications" and "Forensic Science DNA Laboratory Specifications" in July 2002, and in 2003 revised the "Forensic Science DNA Database Field Biological Samples and Sampled Person Information Items and Their Data" "Structure" and "Forensic Science DNA Database Selection of Loci and Their Data Structures" and other industry standards make the establishment of DNA databases in all regions rule-based.
In order to provide technical support to the DNA testing work of each member state and promote the widespread application of DNA technology, Interpol has also set up a DNA expert working group. The expert group, including Chinese experts, is responsible for recommending DNA sampling and evidence collection, and DNA databases. , Quality control, DNA technology training, etc. These international technical exchanges and cooperation will undoubtedly provide a good guide for China's forensic scientific DNA database under construction. The construction of China's DNA database can draw on the successful experiences of various countries and avoid detours.

6 Application of Forensic DNA Database

The scale of DNA database construction is constantly expanding, and the methods are becoming more and more mature, and its huge role has been widely recognized and concerned internationally. If the United Kingdom has a population of 60 million, the average annual number of incidents is about 67.15 million. At present, the United Kingdom has set up laboratories in Birmingham, Wesby and London to carry out the construction of an all-English DNA database. At present, there are 1.5 million personal data and 130,000 on-site physical evidence in the database.
At present, considerable progress has been made in the construction of DNA databases in China. The scale of database construction has continued to expand, and relevant specifications and standards have become increasingly complete, and they have played a huge role in practical applications. For example, the "1, 18" and "1, 10" series of explosions in Shenyang that exploded the country with guns and robbed banknote transport vehicles were merged and eventually detected; some off-site crimes, using different methods, and even passing the database without the knowledge of the local case handling agency Comparing to achieve string of cases and even directly identify the criminal. For example, a series of nine series of rape and homicide cases in Shenyang and Tieling; and a series of five series of rape and homicide cases in Anshan and Yingkou. In some cases, there are no clear clues in the investigation of the case, but after the comparison of the DNA database, the criminal was identified in the criminal record database and the case was cracked.

7 Important Issues in Building a Forensic DNA Database

Establishing a national DNA database is a huge project that requires a certain amount of time and requires full cooperation among courts, DNA laboratories, the legal profession, the government, and legislators. Databases must have many prerequisites before they can be created and used. For example: each region participating in the construction of the database uses common DNA markers and standards to enable comparison of results entered into the database; standardized software enables data exchange between laboratories; and a quality assurance system that allows everyone to trust the experimental results with each other. For the construction of DNA databases, there are many important issues worth exploring.
7.1 Quality assurance system of DNA database <br /> Quality assurance is very important during the construction of DNA database. Faced with a large number of samples in the process of database construction, this means that it is almost impossible to correct individual data in the database, so all data and data that will enter the database are required to be very accurate. If the DNA map entered into the DNA database is inaccurate, it will not be able to obtain a meaningful match. This requires laboratories to operate strictly in accordance with quality control guidelines, and the laboratory's operating procedures must be submitted for review before the quality of the data entered in the database can be guaranteed. At the same time, determining common STR genetic markers with good gene frequency distribution, establishing clear test standards, and strengthening technical support, supervision, and management are even more essential for database quality assurance. Instruments, reagents and personnel are the basis of quality assurance standards. The DNA database expert committee shall regularly review and ensure the quality of the inspection. To strengthen the standardized management of laboratories requires laboratories to operate strictly in accordance with quality control guidelines, which is the premise of resource sharing between different laboratories. When new equipment or newly improved DNA identification laboratories are in place, they must be forward-looking, fully consider the need to establish a DNA database, and choose reasonable equipment. Do not ignore China's national conditions and blindly pursue new equipment and new equipment. Only by eliminating the barriers under a unified standard for DNA data in all places can real sharing be achieved and the value of DNA technology be fully utilized.
7.2 Confidentiality issues < br DNABecause DNA testing is a human biological specimen, which involves sensitive privacy rights, and DNA contains all human genetic information, the genetic characteristics of individuals revealed by DNA testing may lead to job selection, insurance restrictions, and even discrimination Such issues involve complex legal, moral, and human rights issues. Therefore, even if a forensic scientific DNA database is established for the purpose of investigation, the extracted materials must be legal, and the confidentiality of stored DNA information cannot be ignored. In these respects, we can also learn from the experience of Britain and the United States.The April 1995 Regulations on Sample Extraction became British law, marking the beginning of the establishment of a DNA database.The United Kingdom's Criminal Justice and Public Order Act provides the following three Objects of construction: night thieves, sex offenders, and violent offenders, but if it is of investigative significance, the police can also submit other samples with recorded offenders. However, the police are required to distinguish between personal privacy and non-personal privacy when taking samples of individuals. It also stipulates that when a person is found guilty or detained under the law of security, or belongs to a closely linked suspect group during the investigation and trial of a case and one or more of them are found guilty or detained, The data will be put into the national DNA database. When the suspect is found to have nothing to do with the case, or the person has died, or the sampling purpose is only to clarify the facts and no one is found guilty, the DNA typing data will be cancelled . The FBI's DNA database contains only the index number and DNA information data. There is no name, address, race, and case. The details are stored in the state laboratory. When the same is identified, further details can be provided. However, China's current DNA database stores natural information and DNA data of people. The confidentiality of data may cause legal disputes. These issues that may cause controversy must also be considered by the legal profession and legislators.
7.3 Search and match operations < br As the size of the DNA database continues to increase, its value as an intelligent tool is also increasing, but it also brings the problem of search speed. In addition, because the STR kits provided by various manufacturers may have different PCR primer designs for the same locus, there may be cases where using this primer to amplify invalid alleles, and another primer may be normal, so This can lead to inconsistent results due to the use of different kits. This problem can be solved by using a loose search operation mode. For example, when the US CODIS system searches for 26 possible alleles at 13 STR loci, the algorithm and matching scale are appropriately relaxed, and 25 of the 26 alleles match the matching requirements.
The laboratory's detection capabilities are different, especially their ability to detect micromutation OFF-LADDER alleles is uneven. The alleles obtained in one laboratory with a TH01 locus of 8.3 can be compared with 8.x and other in other laboratories. For allele 9 matching, similar problems should be considered in the search algorithm.
7.4 The establishment of a national court scientific DNA database and the need to strengthen computer network management DNA database software is one of the decisive factors for the success of database construction and for ensuring the stability and function of the database. In this regard, the domestic DNA database software compiled by China is not inferior to foreign software, but it also needs to be continuously improved according to the actual situation. In addition, the realization of remote case resolution is a new issue facing China's public security science and technology development at this stage. At present, DNA databases have been established on a large or small scale throughout the country, but it is still difficult to fully share database resources in various places. This has something to do with the imperfect computer network management. Therefore, it is necessary to strengthen the construction of public security communication special network and database software development, and improve the network layout, data transmission and query methods.
7.5 Technological Update DNA technology develops with each passing day. The DNA database must also maintain the ability to update and become a dynamic and tolerant system in order to maintain its vitality. In improving the efficiency of building a database, the key lies in improving the degree of automation and updating technology. The DNA chip can process and analyze a large number of DNA fragments at the same time, and its comprehensive efficiency is unmatched by current conventional technology. The DNA chip is used to detect a more abundant genetic marker system in the genome-single nucleotide polymorphism (SNP) It is also gradually favored by the forensic community. SNP chips are being developed for forensic applications. In addition to the advantages of high throughput and high efficiency, it is more meaningful that SNP can test extremely degraded DNA, so that samples that cannot be tested can be successfully used, so it is expected to store SNP in future DNA databases. Polymorphism information. Another development direction of new technology is to establish marker systems that can identify individual appearance features, such as identifying genetic marker systems such as skin color, hair color, height, and weight. These marker systems may be based on point mutations or deletions, and are more suitable for automation. analysis. Storing such genetic marker information that identifies individual appearance characteristics in future DNA databases will be more effective in guiding reconnaissance directions.
The forensic DNA database follows the trend of the development of public security work towards intelligence, networking, and automation. With the development of DNA analysis technology, more and more individual information can be obtained from human biological samples. The national forensic science DNA database must maintain the ability to update, so that new technologies that are continuously developed can serve the DNA database in order to maintain its vitality. Become a powerful and powerful tool for crime detection. DNA databases should also be combined with other analytical techniques to expand their application space. In addition, international DNA technology cooperation can also make the development and application of DNA databases more extensive, making it more effective in combating crime and serving the society. ^[2]

Important concepts

1. Forensic medical expert: refers to a person hired and commissioned by judicial organs, arbitration organs or other administrative organs, enterprises, institutions, and people's organizations to use expertise or skills to identify and determine medical problems in a case.
2. Evidence: Public security organs, people's procuratorates, people's courts and other subjects used to prove the objective existence of the true situation of the case in the litigation process.
3. Expert Witness: Compared with ordinary witnesses , their appraisal conclusions and opinions are expert testimony, not legal evidence, and their statements with ordinary witnesses are considered in terms of logical thinking, psychology, litigation status and legal status There is no essential difference between the two, only the difference in the level of knowledge they have.
4. Trial ability: refers to the ability of criminal suspects and defendants to understand their status and rights in criminal litigation activities, understand the meaning of the litigation process , and be able to exercise their own litigation rights.
5. Civil capacity: Refers to the qualification of a civil subject to participate in civil activities, obtain civil rights, and assume civil obligations by his own actions.