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Documentation, Collection, and Preservation of DNA Evidence

Deoxyribonucleic acid, shorted as DNA, is an organic chemical of nucleotides found in almost all living organisms. DNA is used for identification since two or more people cannot share the same DNA except identical twins. Nearly all the cells in a person’s body have the same DNA; therefore, it provides highly accurate matches to a person or an organism under study or investigation (Ronit Dey – (B.S in Zoology), 2020). Those features give every person distinct features that make DNA an essential tool in solving crimes, as biological samples collected can only link one person to a crime. Collecting samples from a crime scene can help exonerate a wrongfully accused person and link the crime perpetrator to be tried and sentenced. Biological analysis and sample processing also help determine parentage between an adult and a child, genealogy tests, and genetic screening for disease.

As such, collecting DNA from a crime scene is an essential procedure in crime investigations and must be conducted correctly. The preciseness in collecting and preserving DNA evidence is to eliminate errors that may arise from the transfer of DNA to a crime scene (Press, 2019). In a crime scene, three parties are involved, one of which may be included regarding the collection of DNA evidence. These are the victim, the suspect, and the witness. The witness may be exempted unless found at the crime scene or a location in connection with the crime. The victim and the suspect are, however, primary in investigations and therefore have to undergo DNA collection procedures to check for transfer of biological evidence.

There are various ways in which biological evidence is transferred from a suspect to a victim or a crime scene. These organic natural body materials can link a person to another individual, an object used to commit a crime, or a location. The first way biological evidence can be transferred is through direct deposit. Direct deposit can result from agents that carry DNA samples such as hair, blood, semen, and other body fluids, which are transferred directly from a suspect to a victim, a crime scene, or an object used to commit a crime. Fluid or liquid biological specimens, such as blood, can be deposited directly and adhere to the surface (Author links open overlay panel Roland A.H. van Oorschot a b et al., 2018) .non. Fluid ones, such as hair, can be transferred through direct contact. i.e., DNA deposited on a victim, suspect, object, or crime scene.

Another way in which biological evidence can be transferred is through secondary transfer. Fluid and non-fluid biological specimens are transferred to a victim, a suspect, an object used to commit a crime, or a scene through an intermediate medium. Therefore, direct contact between the source and the target surface is eliminated in secondary transfer. The secondary transfer is as necessary as direct deposit, as positive results are enough proof to directly link an individual to a specific crime scene.

Documentation of DNA evidence is the process of classifying and annotating photographs of evidence samples. It can also be official information, evidence, or records of and examples collected. Documentation of evidence is vital for legal purposes and scientific purposes. Forensic science has several documentation means, and all of them are required for lawful purposes. Specimens collected for evidence can be documented at the crime scene by photographing and videotaping the evidence before moving, touching, or even collecting. The next step is noting the condition of the collected evidence and then sketching the space occupied by each piece of evidence concerning other objects at the crime scene. The last procedure is noting and outlining the state of the biological evidence.

Documentation of evidence is also done at the forensic laboratory to keep records for court purposes. For proper documentation, the following procedures are done. The package is labeled with unique identification markings, lab case number, and date; it is then sealed in the right conditions for the exhibits. The evidence is photographed and checked against the submission form to ensure the item’s description is correct. DNA evidence is biological specimens that carry DNA samples collected from a crime scene for forensic analysis. For DNA evidence to meet legal requirements for use in a court of law. There are standard procedures to be followed. These procedures are; the documentation procedure of the evidence, the handling and packaging of evidence, the number of specimens to be collected, and the type of evidence to be collected. Of importance is the technique used to collect the various biological materials that carry DNA samples and, finally, the preservation of collected evidence. These are critical because different kinds of specimens can be managed at different crime scenes, and various representatives require other procedures of collection and preservation methods before analysis.

The following step-by-step procedures are observed while collecting and preserving DNA evidence recovered at crime scenes. Blood specimens still in liquid form can be retrieved by soaking them with a clean cotton cloth, a sterilized syringe, or a pipette. The samples retrieved are labeled with specifics like a case number, collector’s name for accountability, location, time, and date distinctive to a particular crime. Objects or garments with wet bloodstains are air-dried and packaged in plastic containers. The plastic container/bags should not be airtight to avoid moisture retention hence sample deterioration.

For Blood samples in water or other clear liquids, the collection is done immediately before further dilution. If possible, the samples are frozen and submitted as it is to the laboratory for analysis. Wet bloodstains can also be found at a crime scene. Garments or objects with wet bloodstains are allowed to air dry and collect as it is in a clean plastic bag. However, the collection of dried bloodstains differs from wet and liquid blood samples .dried bloodstains on removable things like garments and other moveable items are collected separately, as also the whole item. Dried bloodstains on things that are indivisible, large or immovable objects in which the specimen cannot be scrapped, documenting and sketching of blood patterns are done. The bloodstain is first eluted onto a tidy switch, moisturized with water then dried. After drying, it is packaged in a paper fold, placed in an envelope, sealed, and correctly is advisable to obtain control by repeating the same procedures on the other/adjacent unstained surface area containing the dried bloodstain.

Small dried blood spatters are always challenging to collect, and the tape lift method removes them from their surfaces. A clean fingerprint tape lifts the small blood splatters from the surface after adequately documenting the crime scene. Each piece is packaged and labeled separately. Another type of biological material that can be collected is semen or seminal stains liquid semen. In this case, the first step is to document the seminal evidence by videotape, notes, sketching, and photography. The evidence is then transferred to a sterilized test tube. Labeling is done, and the specimen is stored in a refrigerator awaiting analysis. Seminal specimens from sexual assault victims are collected through established procedures by a medical examination of sexual assault victims in the hospital.

For seminal evidence on nonabsorbent surfaces such as metal surfaces, the first step is documentation of the seminal stain evidence, .then scrapping it off onto a clean paper using a sterile scalpel into a druggist fold container. The procedure is repeated using a new or the same scalpel but washed and sterilized between procedures to avoid contamination. Seminal evidence stained on objects that can be cut, i.e., beddings, are documented, and then by use of a clean pair of scissors, the stained area is cut from the rest of the surface. Each cut surface is placed separately on a clean piece of paper. A druggist fold package and then secures the evidence to avoid any contamination.

Biological evidence always collected is human hair. These can be reserved using a clean pair of forceps. Care should be prioritized to prevent damage to any hair root tissue. The hair evidence collected is grouped and packaged separately, sealed, and labeled correctly. Saliva, urine, and other body fluids are also critical DNA evidence. When liquid, they can be collected by transferring samples into a clean, sterilized container, i.e., glass or plastic. The container is then sealed, appropriately labeled, and refrigerated on the way to the laboratory. For saliva or other body fluid stains, the stained surface is collected as it is, or for the case of immovable objects; the dye is scrapped off or cut off. They are then collected in a clean druggist fold and stored temporarily in a second paper, sealed and correctly labeled.

The last biological materials that can be used as DNA evidence are organs, bones, and tissues. The samples collected can be fresh or old, depending on the time of collection. Each item ordered as evidence should be documented by photography or sketching and described in notes as added information. They are picked using a pair of sterilized forceps and placed separately in clean containers without any added fixatives. For old evidence, specimens are sketched and photographed before collection. The space occupied by the sample evidence is outlined to the other objects in the scene, a pattern formed, the specimen’s shape drawn, and the size weighed as part of the documentation process (McCombes, 2023). After wearing gloves, they are handpicked, and any evidence connected is collected together. Each item is managed with a different pair of gloves to avoid contamination.

When investigators collect a piece of evidence at a crime scene, it is placed in a paper bag, or an envelope .this is because paper bags try to keep the biological materials in the DNA samples at room temperature. Exposing them to direct sunlight or warmer conditions or even storage in plastic bags that retain moisture can damage the evidence. After that is the conduction of chain of custody procedures, which label the packages with details such as material components, location retrieved, and destination for analysis. Such procedures account for the integrity of the samples from collection to analysis.

To compare the suspect’s or victim’s DNA profile to the specimen retrieved at the crime scene, the forensic technician requires their biological data and reference samples for direct comparison. The reference samples are collected from victims through their corporation, or, if otherwise, a court order is required. The specimen collected then undergoes some procedures. The first is extraction, which is done to extract the DNA from the body cell. After that is quantitation to determine how much of it there is. Quantification is vital in the case where multiple comparisons will be made. The next step is amplification, producing numerous copies of the DNA to characterize it. They are then followed by the separation of amplified and product for subsequent identification. Followed by that is the analysis and interpretation, comparing evidence samples to known profiles qualitatively and quantitatively (Pelz). The last process is reviewing laboratory reports for technical security, quality, and standardization.

To conclude, it is evident that for DNA evidence to be valid for legal or scientific purposes, some steps follow a systematic order from documentation to the preservation of sample evidence. World international conventions have formed the measures to handle evidence similarly in countries covered by these conventions. These procedures help solve the world crisis through international investigative bodies with jurisdictions in all counties. Doing so ensures standardization hence the same level of fairness is applied when conducting investigations on a crime committed by a suspect in a particular country or a foreign country. DNA evidence is a milestone in solving crime solutions in conjunction with forensic science; with continued research in that field, there will be a reduction in crime rates and the prevalence of justice.


Ronit Dey – (B.S. in Zoology). (2020, October 5). Do all cells have DNA? Do all body cells have the same DNA? ONLY ZOOLOGY – (Know, Learn, Explore Zoology).

Press, R. (2019, April 3). DNA mixtures: A forensic science explainer. NIST.

Author links open overlay panel Roland A.H. van Oorschot a b, a, b, c, d, e, f, g, AbstractUnderstanding the variables impacting DNA transfer, Akutsu, T., Berge, M. van den, Haas, C., Hanson, E., Virkler, K., Sijen, T., Finnis, J., Linacre, A., Quinones, I., Zoppis, S., … Phipps, M. (2018, October 26). DNA transfer in forensic science: A Review. Forensic Science International: Genetics.

Pelz, P. B. (n.d.). Research methods for the Social Sciences. Chapter 13 Qualitative Analysis | Research Methods for the Social Sciences.

McCombes, S. (2023, March 27). Sampling methods: Types, techniques & examples. Scribbr.


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