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Criminalistics – Crime Scene Investigation

Criminalistics – Crime Scene Investigation


“A case is only as strong as its evidence” (Maria, 2009). This statement emphasizes the significance of evidence in correlation to investigations. Evidence is the information used to make a judgment or a conclusion. It is presented in addressing questions that have been intentionally posed because an institution views them as important. Acquiring good evidence includes ensuring that it is purposeful and designed to address specific questions, has been broken down and reflected upon, and is not only reviewed in its unanalyzed or raw form but is cumulative and supported by different sources of data. In the pursuit of justice, evidence is the foundation used to create the arguments made by both sides. The success of crime investigations relies on determining if a crime was committed by carefully analyzing the evidence presented. It is important to consider all relevant evidence due to the fact that offenders may leave behind signals of information that can solve a case. Important information includes eyewitness descriptions, fingerprints, or a murder weapon. The collection of evidence at a crime scene is considered to be one of the most vital roles of an investigator. This paper presents a lesson plan for a crime lab, including investigators who will be required to report to crime scene units in their first assignments as crime scene investigators. The lessons will mainly cover the two categories of physical evidence used for identification or comparison purposes, the differences between class and individual characteristics of physical evidence, the importance of class characteristics, and why their analysis can narrow the scope of the investigation for crime scene investigators.

Lesson One: Categories of Physical Evidence

Physical evidence refers to any physical objects associated with a tort or crime. It can be collected in various forms to help in the investigation of a tort or crime if the right steps are taken to identify, collect and store it (Greene, 2006). The main ways in which this type of evidence can help in an investigation include helping in the reconstruction of a crime scene, establishing whether a crime occurred or not, connecting an individual with a crime scene or a suspect, creating investigative leads for investigators, providing evidence to connect rape cases or serial homicide and offering facts to a jury which may help in determining whether an accused person is guilty or not. One of the benefits of physical evidence is offering tangible objects for the jury to consider. The second benefit is that it cannot be distorted by a defendant. It is additionally not affected by memory loss, and its credibility can be tested by an independent expert with the permission of a defendant. The main types of evidence in criminal investigations are biological and impression evidence.

Biological Evidence

Biological evidence is defined as biological material samples such as bones, saliva, hair, and blood or evidence containing biological material (Lee & Harris, 2011). The analysis of biological evidence includes DNA analysis, toxicology, anthropology, and histopathology examination. Toxicology includes analyzing biological samples such as urine and blood to detect, identify and quantify significant toxicology substances and the interpretation of the results to determine the cause of poisoning or death and the abuse or use of drugs. The most common analysis in toxicology is the analysis of blood ethanol and the analysis of pesticides and carbon monoxide to determine if there was poisoning. Histopathology examination includes analyzing tissue during biopsy or post-mortem and taking it through various processes before examining it under a microscope. Histopathology examinations help in seeing changes from the body to the cell level.DNA analysis is mainly limited to biological samples based on the fact that all biological evidence is applicable for DNA analysis except the body fluids without nucleated cells, such as serum, sweat, and tears. Anthropology includes the analysis of bones to determine the approximate age, gender, and height of a victim, differentiate between animal and human bones, and determine the cause of death through bone injuries.

Impression Evidence

Impression evidence is defined as the markings created when one object comes into contact with another object creating a kind of print or indentation. The main types of impressions are tyre marks, footsteps, and other markings made by tools (Lee & Harris, 2011). They can be found on various surfaces, including carpets, dust, or blood. Collection of this category of evidence is a specialized forensic task because it cannot be carried away from the crime scene. This type of evidence may be found in either two or three dimensions. For instance, a shoe can leave two dimensions on a surface due to the static charge on the sole, leaving the particles on the surface. A three-dimensional process occurs when the surface the shoe is passed over is soft, and the sole sinks in it. The method used in collecting impression evidence mainly relies on how the impression was made and the surface on which it was made. The impression should be photographed on-site and made a plaster. The impression may also be dusted using fingerprint powder. An investigator may also use dyes to see impressions on non-porous surfaces, but such impressions may be fragile. Investigators may also use electrostatic treatment to lift the impression onto a more stable surface so that it can be transported to the lab.

Lesson Two: Differences Between Class Characteristics of Physical Evidence

Class features are the physical evidence properties that can only be linked to a group instead of one source. If evidence is considered to have class features, it may be used as a strategy for reducing the number of suspects, but it cannot be directly connected to a single person or source. Class evidence includes paint, fibres, and blood type. Class characteristics can be used to establish things such as types of automotive paint or blood types of a group of people but cannot produce an individual identification or specific match. Class evidence is mainly used to narrow down a list of credible sources. According to Saferstein (2012), The main challenge associated with the use and collection of evidence with class attributes in court arises from the inability of investigators to assign approximate or precise probability values when conducting a contrast of more class evidence (Ogle, 2006). For instance, a forensic investigator investigating a murder may not be able to determine the likelihood that a nylon fibre in a crime scene came from a specific sweater because we are living in a society that relies on goods that are produced in large numbers. Individual characteristics are, on the other hand, physical evidence properties that can be linked to a shared source with an elevated level of certainty. Individual evidence includes anything containing fingerprints, tool marks, and DNA. In investigations, matching ridge attributes of two fingerprints and matching handwriting and footwear impressions can be considered to be physical evidence with individual attributes because the evidence properties gathered from the crime scene can be attributed to a specific perpetrator with a high uncertainty level. The main challenge associated with individual characteristics is the inability of investigators to state with numerical exactness the likelihood that the analyzed specimen is of a shared origin (Ogle, 2006). Most forensic investigators using evidence with individual attributes work from the assumption that the likelihood that the specimens are of shared origin is so high to the extent of challenging mathematical computations or human understanding, but the examiner may face challenges in verifying such an assumption beyond any reasonable doubt in court. As such, it may be hard to authenticate the conclusion of the same origin of evidence-based probability computations or the experience of the forensic examiner.

Lesson Three: The Importance of Class Characteristics and Why Their Analysis Can Narrow the Scope of the Investigation for Crime Scene Investigators

The value of physical evidence with class characteristics is based on its ability to offer support of events with a date that is free from human bias and error. If evidence incorporates class features, it may be used as a mechanism of reducing the number of defendants, but it cannot be directly connected to one source or person (Ogle, 2006). These class features may help the investigator limit their focus to suspects with that class of description. It is not a positive identification of evidence to any specific suspect, but it allows the probable elimination of suspects with the same attributes. Using this type of examination, an investigator at the crime scene may find a suspect’s attributes showing unique attributes. If a suspect with similar attributes is found near the crime scene, the level one observation will offer strong inferred evidence to help in creating reasonable foundations to suspect that this individual was part of a crime.


Greene, J. R. (2006). Encyclopedia of police science: 2-volume set. Routledge.

Lee, H. C., & Harris, H. A. (2011). Physical evidence in forensic science. Lawyers & Judges Publishing.

Maria, T. E. (2009). Careers in Forensics: Analysis, Evidence, and Law. ERIC – Education Resources Information Center.

Ogle, R. R. (2006). Crime scene investigation and reconstruction: With guidelines for crime scene search and physical evidence collection. Prentice Hall.

Saferstein, R. (2012). Forensic science: From the crime scene to the crime lab (2nd ed.). New York City, NY: Pearson.


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Criminalistics - Crime Scene Investigation

Criminalistics – Crime Scene Investigation

You are an instructor for a state crime lab. It is your responsibility to start the basic training for the new candidates who, upon completion of their training, will report to crime scene units in their first assignments as crime scene investigators.
• Your first lesson involves explaining the 2 categories of physical evidence used for identification purposes or comparison purposes.
• Your second lesson is explaining the differences between class characteristics of physical evidence and individual characteristics of physical evidence.
• Your third and final lesson is to explain the importance of class characteristics and why their analysis can narrow the scope of the investigation for crime scene investigators.
In a 4–6-page paper, prepare your 3-part lesson plan on the instruction you would provide to new crime scene investigator candidates for the aforementioned lessons.

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