Identification, Collection and Preservation of Evidence


For five types of evidence— drugs, firearms, glass, paint, and tool marks—the processes of identification, collection, and preservation were explained. For each type, it was established how to detect relevant evidence at the crime scene and judge its importance for further investigation. Also, necessary precautions and appropriate procedures for gathering evidence of all five types were described. Finally, it was explained how to deliver the evidence to the laboratory in a way that enables successful forensic analysis. Several general principles of collection and preservation were found, including keeping evidence intact (except for firearms that should be unloaded for safety) and packaging everything separately.


Upon the initial walk-through at the crime scene, the next step is to properly identify and collect evidence and to ensure that it will be appropriately preserved for further analysis. The general crime scene procedures are similar for different types of physical and trace evidence, and the general principle is the same—to collect everything that can assist in solving a crime and in making sure that it is unaltered and not contaminated so that nothing interferes with analyzing it—but the specificity of different types of evidence should not be overlooked because they may present different complications on the collection and preservation stages (Saferstein, 2013). Five types of evidence were chosen to describe their proper identification, collection, and preservation: drugs, firearms, glass, paint, and tool marks.


Drugs are defined as “any substance in violation of laws regulating the sale, manufacture, distribution, and use of drugs” (Saferstein, 2013, p. 81). Various types of regulated substances exist, and drugs come in many forms, which is why an investigator may overlook the presence of drugs at the crime scene. However, “common sense is the best guide in such situations” (Saferstein, 2013, p. 267). Anything that can be suspected to contain illegal substances should be treated as evidence. This may include powders, powdered crystals, granular substances, pills, dried leaves and other plant parts, and suspicious liquids (Millen, 2013). The presence of certain objects associated with drug use and drug production can indicate the presence of drugs at the crime scene, too; these objects include used syringes, burnt spoons, manually rolled cigarettes, laboratory equipment, and razors.

The collection of drugs at the crime scene is estimated as relatively simple, but several complications may occur. First of all, different packaging may need to be applied to different types of drugs due to different chemical and physical characteristics. Labeling evidence before delivering it to the laboratory is necessary. Moreover, it is recommended that investigators, when collecting substances suspected of being drugs, indicate for analysts the context of the collection, i.e., where exactly the sample was collected and what surrounded it. The practice of working with evidence shows that this indication can significantly reduce the time needed by analysts to identify substances (Saferstein, 2013). Since the list of controlled substances in the United States is “extremely flexible” (Saferstein, 2013, p. 268), the illegal status of certain substances may be reconsidered at any time, but any evidence suspected of being a dangerous drug that is confirmed to cause physical and psychological addiction should be collected with proper tools, including bags, envelopes, and possible scalpels or razor blades if suspicious substances need to be scraped off a surface.

Being organic substances or synthetic chemical compounds, drugs are more likely to be contaminated than some other types of physical evidence, which is why their preservation is crucial. To avoid loss or cross-contamination, drugs should be packaged reliably, and their original packaging normally meets this requirement of preserving the original content (Baxter, 2015). Complications may arise with volatile drugs, such as solvents used for sniffing. A container for them should be airtight to ensure that the solvent does not evaporate. In case the collected substance’s actual component that is regulated as a drug is lost, the substance may become inadmissible in court.


Important pieces of evidence that can be collected at a crime scene are any types of firearms as well as discharged or intact ammunition suspected of being involved in a crime. Firearms usually come in two forms: handguns and long guns. Firearms identification is the study of weapon characteristics that allows identifying whether particular ammunition items detected at the crime scene were fired from certain firearms. The inner surfaces of gun barrels, known as bores, are rifled, i.e., spiral grooves are impressed on them, for the purpose of spinning a bullet when it is fired. The striation of rifled barrels, i.e., the pattern of striae, grooves on the bore, is unique, which means that markings on a bullet can theoretically allow identifying the gun from which it was fired (Saferstein, 2013). Detecting firearms and bullets or cartridges at the crime scene rarely involves complications.

Firearms may have important evidence on them, such as fingerprints, which is why the specialist who collects them should wear latex gloves and hold them carefully in the areas that were unlikely touched by a person who fired them. This will prevent scratching, contaminating evidence with grease, the presence of investigators’ fingerprints on a gun, and other possible complications. Also, firearms may have substances on and inside them that can indicate when guns were fired, which is why it is important to package these pieces of evidence into plastic bags. If bullets need to be extracted from any surfaces at the crime scene, an investigator should use tweezers (if the bullet is close to the surface), but the extraction should be carried out carefully not to scratch the bullet (Fisher & Fisher, 2012) because it may display a pattern that will allow identifying the firearm from which it was fired.

Although firearms are less vulnerable than some other types of physical evidence, such as chemical compounds or organic substances, it is necessary to deliver them to the laboratory as soon as possible because the early analysis is more likely to indicate when a gun was fired. To prevent contamination and physical damage, firearms and ammunition should be packaged in plastic bags. However, before this, it is necessary to unload the weapon to prevent accidental discharge because safety is the main consideration (Saferstein, 2013). Concerning bullets, they need to be wrapped in tissue paper and put into an envelope; the wrapping is needed to preserve minute evidence that may be present on the bullet, including chemical substances or fibers. Under normal conditions, not many factors can cause the inadmissibility of firearms and ammunition in court.


There are two primary purposes of forensic analysis of glass fragments or particles: first, they may contain minute traces of evidence indicating who contacted this glass; second, they may be analyzed for their origin. The former is needed in such cases as breaking and entering, burglary, or similar cases where offenders break glass with illegal intentions. Fragments of broken glass may contain fibers of suspects’ clothes, drops of their blood, or other indicators of who broke the glass. In terms of establishing the origin of glass fragments, it may be needed in hit-and-run accidents for identifying a vehicle involved in an accident (Saferstein, 2013). Also, bullet holes in glass may be subject to forensic analysis. Identification of glass fragments at the crime scene rarely involves complications.

Concerning the collection of glass evidence, the first rule for an investigator is to gather all the glass fragments that can be found at the crime scene. For example, in investigations of hit-and-run accidents, collecting all the shattered parts of the headlight and reflector lenses of a vehicle that escaped the accident scene is crucial because matching these fragments with glass that remained in the suspect vehicle can become ultimate evidence for placing the vehicle at the crime scene. Therefore, any shattered glass should be appropriately collected if “even the remotest possibility exists that fragments may be pieced together” (Saferstein, 2013, p. 362). Since glass fragments can be sharp and dangerous, appropriate safety measures should be taken by an investigator to prevent cuts and breakages of packaging. Glass should be collected carefully to prevent further breaking and placed in paper bindles and then in envelopes, boxes, or cans (Spear, Rush, Massetti, Weigand, & Traughber, n.d.). Bindles are needed to prevent loss and edge damage.

Concerning preservation, glass is known to be chemically inactive, i.e., not many substances can affect the composition of glass, and it does not react with most substances that it can contact under normal conditions. However, glass is fragile, which is why it is needed to place large fragments, especially those that are not flat, in boxes to prevent further breaking. Also, despite the resistance of glass to chemical influences, traces of evidence that can be found on glass may be affected by contamination, which is why preservation from contaminants is still required.


Paint is important evidence because it covers various surfaces and can be easily transmitted from one object to another, either in liquid or dried forms, thus indicating a contact and possible involvement in a crime. Identification of paint traces at the crime scene is often associated with the search for paint chips, i.e., small particles of dried paint that peeled off a surface. Even the smallest paint chips should be collected because as small amounts of them as 20 micrograms (Saferstein, 2013) can be used in the analysis. Therefore, identification may require scrutiny, but it is justified by the importance of this evidence for placing suspects at the crime scene.

Saferstein (2013) particularly describes the procedures of collecting paint in investigating hit-and-run accidents. In these cases, paint chips are usually found on the clothes of people involved in the accident, on vehicles, on near them. It is especially stressed that paint chips should be kept intact, which is a rather difficult task due to their thinness and fragility, which is why the collection should be carried out “with the utmost care” (Saferstein, 2013, p. 350-351). A way to do it is to use tweezers or a piece of paper to pick paint chips up. Glass and plastic vials should be used as containers. Also, if the paint is smeared on an object, it is better for an investigator to package the entire object and deliver it to the laboratory than to try to scrape paint off. In hit-and-run accidents, paint from undamaged parts of suspect vehicles should be collected, too, for the purpose of comparison.

In terms of preservation, it is noteworthy that paint can be contaminated by the presence of various chemicals, which is why it is necessary to isolate it from exposure to any substances until it is delivered to the laboratory (Fish, Miller, Braswell, & Wallace, 2013). Also, when collecting different samples (from damaged areas, undamaged areas, deeper layers of previous paint, and so on), an investigator should make sure to use disposable scalpels every time to prevent cross-contamination of different paints, thus preserving them for analysis.

Tool Marks

On various surfaces and objects at the crime scene, marks can be found that can be attributed to something that served as a tool in the investigated crime. These marks may include “impression, cut, gouge, or abrasion“ (Saferstein, 2013, p. 214). Identifying tool marks can be challenging because the tool itself may be absent, which significantly increases the number of mark types to be searched; besides, it is not always evident which marks at the crime scene are relevant to the crime (by being caused by the contact with an instrument of crime) and which may be irrelevant because they had appeared before the investigated crime was committed. In identifying a tool mark, it is important that an investigator should not fit the suspect tool into the mark because any contact will alter the mark and complicate or make further analysis impossible.

For the collection of evidence, the entire object with a tool mark should be packaged and delivered to the laboratory. In case the transportation of such an object is impractical, the mark should be photographed, or a cast should be made with liquid silicone. However, this will significantly reduce the chances of successful individualization of the mark to the suspect tool.

The value of tool marks as evidence is that they allow placing a suspect tool at the crime scene, but in order to prove the connection, both the mark and the tool should be properly preserved, and any contacts between them or between the mark and other objects and the tool and other objects should be prevented. For example, in burglaries, paint found on a tool can serve as valuable evidence, as “paint [chips] adhering to the mark or tool provide perhaps the best example of how the transfer of trace physical evidence can occur as a result of using a tool to gain forcible entry into a building” (Saferstein, 2013, p. 216). Loss or destruction of physical evidence on a suspect tool or a tool mark can make this evidence inadmissible in court.


Five types of evidence have been addressed to determine how they should be identified at the crime scene, collected, and preserved. The types of evidence are drugs, firearms, glass, paint, and tool marks. It has been shown that pieces of evidence may vary to a large extent in terms of difficulty to detect them, process, and deliver to the laboratory. However, there are general principles applicable to all of them: as many pieces of evidence should be collected as possible; everything should be properly labeled and accompanied by some context to facilitate further analysis; evidence should be kept intact (with the only exception of safety considerations: firearms found at the crime scene should be unloaded); and separate packaging is required in most cases to prevent cross-contamination. It can be concluded that a proper and thorough approach to the identification, collection, and preservation of evidence is crucial in solving a crime.


Baxter, E., Jr. (2015). Complete crime scene investigation handbook. New York, NY: CRC Press.

Fish, J. T., Miller, L. S., Braswell, M. C., & Wallace, E. W. (2013). Crime scene investigation (3rd ed.). New York, NY: Anderson Publishing.

Fisher, B. A., & Fisher, D. R. (2012). Techniques of crime scene investigation (8th ed.). New York, NY: CRC Press.

Millen, P. (2013). Crime scene investigator: True stories of forensic detection. London, UK: Constable & Robinson.

Saferstein, R. (2013). Forensic science: From the crime scene to the crime lab (2nd ed.). Boston, MA: Pearson.

Spear, T., Rush, J., Massetti, J., Weigand, J., & Traughber, M. (n.d.). Evidence packaging: A how-to guide. Web.