Theorem of Uniqueness in Forensic Sciences: A New Approach
Written by Mukesh Sharma   

FORENSIC SCIENCE requires the concept of uniqueness. For this purpose, it is supposed that a uniqueness theorem should be applicable in forensic sciences. On the basis of fundamental mathematics and physics, one can easily evaluate the theorem of uniqueness in forensic science.

This article appeared in the July-August 2020 issue of Evidence Technology Magazine.
You can view that issue here.

In mathematics, a theorem states the uniqueness of a mathematical object, which usually means that there is only one object fulfilling given properties, or that all objects of a given class are equivalent. In basic physics, we study the uniqueness theorem which states that there can be only one solution of Laplace's equation that satisfies the prescribed boundary conditions. Similarly, one can evaluate on the basis of experience and observations in the field of forensic science that every crime scene, tool mark, and other physical evidence must have unique characteristics.

By our experiences and observations, the theorem of uniqueness for forensic science is termed as “Every crime scene has unique evidence, even though the crime scene is similar in nature or modus operandi. The physical evidence, tool marks, and patterns must be unique in nature.” To prove the statement, we provide in this article a survey of our earlier studies and evaluate the theorem of uniqueness in field of forensic science.

Evidence tells a story, helps an investigator recreate the crime scene, and establishes a sequence of events. If physical evidence is analyzed and interpreted properly, it helps the investigation take the right path from the crime scene to the courtroom—where it is more reliable than testimonial evidence. Therefore, physical evidence is often referred to as the “silent witness”1. Crime scene classification labels the site of the original or first criminal activity as the primary crime scene and any subsequent crime scenes as secondary2. Modern classifications of the crime scene are summarized in Figure 1.

Figure 1. Categories of crime scene with uniqueness concept.

The fundamental principle of forensics is that every contact leaves a trace. Whether the contact is between a person and another person, between a person and a vehicle, or between a vehicle and a location—the trace is always unique. Forensic investigators identify the individuality of those traces and analyze them to explain what has happened. Evidence at crime scenes may include:

  • Biological samples such as DNA from blood, semen, saliva, hair, fingerprints, body-part prints, urine, or teeth.
  • Fibers such as pieces of material torn from clothing, or pieces of weapons broken during an attack.
  • Photographs, videos, drawings, and plans.
  • Documentary evidence such as receipts, travel tickets, or bank statements.

Some crime scene investigation techniques are complicated and resource-intensive, and therefore may not be available to all investigators. But while visiting a crime scene, a forensic expert should search for abnormal or unexpected elements in the space in order to identify the uniqueness of the physical evidence as the silent witness3. A standard proposed way for forensic investigation by an expert to analyze a crime scene is explained via the flow chart shown in Figure 2.

Figure 2. Examination of crime scene

Crime scene investigation may include a combination of the following types of incidents and examinations:

  • Accidental deaths, which include a multitude of circumstances, and do not exclude misadventure.
  • Suicidal deaths, which include a multitude of circumstances.
  • Homicidal deaths, which include a multitude of circumstances.
  • Sudden deaths, with or without suspicious circumstance.
  • Difficult victim identification, which includes mummification and putrefaction.
  • Disaster-victim identification and dealing with multiple casualties.

These types of crime scenes are always a challenge for the forensic expert visiting a crime scene.

Concept of Uniqueness
In major criminal investigations such as homicides, suicide, rapes, hit-and-run, and custodial death, personnel with more extensive training and experience are likely to be used in processing crime scenes5. In cases of strangulation or hanging, where unmistakable signs of death are observed, the forensic officer at the scene should do nothing to the body. In some cases, the investigation yields results that point directly to and provide solid evidence against the offender. However, all cases are unique in nature and some present very peculiar evidence at the scene. 

Ground to Establish the Uniqueness Concept
A brief survey of various case studies demonstrates the concept of uniqueness between different crime scenes.

Case Study 1In this case study, four family members (a husband, wife, and two young sons) were found dead in their residence. Initially, this case seemed to be suicide, due to the presence of insecticide in the food material available at the scene, and no signs of struggle. After careful scientific observation of the crime scene by the forensic team, several factors (e.g. absence of vomit, no insecticide containers or wrappers at the scene) suggested that this was not a suicide. Due to a large amount of different kinds of medicines at the scene, we advised police to search for a person familiar with the decedents who may have knowledge of medicinal sciences or who may be practicing medicine. On the basis of our direction, the eldest son of the family—who was practicing medicine in another village—was arrested; he finally confessed to the crime. This confession was confirmed through toxicology and a postmortem report showing intravenous injections on all of the victims’ hands.4

Case Study 2 – In this case study (published in Forensic Magazine5), we report an interesting case of murder, involving a young married woman, that was unraveled by the crime scene team. The collection of evidence and the laboratory analysis of exhibits provided the corroborative evidence necessary to prove the victim’s in-laws were trying to mislead the investigating officer by fabricating a story of looting and murder. The entry and exit points and blood analysis proved to be the unique elements of evidence at the crime scene.

Case Study 3This incident6 was reported in the historic fortress of the village Jasaana (Rajasthan, India). As part of some modernization and renovation of the fortress, some arc welding caused a massive explosion. Our team of expert visited the scene and, taking a forensic point of view, calculated the amount of explosive materials and the level of explosion. Based on our observations, we concluded that this explosion might have been caused by gunpowder. Throughout this article we tried to shed light on the features and characteristics of gunpowder explosions, and we performed the first-ever forensic attempt to estimate the amount of gun powder that exploded. It was a unique study into the nature of explosives.

Case Study 4In this study7, we reported the importance of investigating evidential samples obtained at various crime scenes. X-ray fluorescence (XRF) is used widely in forensic science. Its main strength is its non-destructive nature, thus preserving evidence. We analyzed the application of XRF to examine evidence such as the purity of gold and silver jewelry (Indian Ornaments), remnants of glass pieces, and paint chips recovered from crime scenes. The experimental measurements on these samples were made using an X-ray fluorescence spectrometer (LAB Center XRF-1800) procured from Shimazdu Scientific Instruments (Portland, Oregon). The results are explained in terms of quantitative/qualitative analysis of trace elements, and how useful X-ray fluorescence is from a forensic point of view. Trace evidence is the silent witness of this case study covering laboratory examination; even in this case study, the results are unique.

Case Study 5In this manuscript8, the authors analyze a fire incident that occurred in a factory at Nimrana City, Alwar (Rajasthan, India) on October 29, 2007, in which volatile and inflammable chemicals were used as raw material. Safety precautions should be followed as per standard operating procedures in the presence of volatile and inflammable chemicals, but a long-term and experienced laborer can readily bypass the safety precautions and invent shortcuts for routine work—which can result in havoc. Through this paper, the authors explain the data related to the case that helped in reconstructing the dynamics of the accident. We also suggest methodology to investigate cases related to fire or arson. Using the methodology in the investigation of fire cases, we have proposed, the reported items of evidence were unique.

Case Study 6 – In this very interesting case study9, we have tried to explain the importance of the scene examination and preservation of the crime scene. Through this paper, the author explains the circumstances that can change the public’s perception. That is, by using the forensic expert’s view, proper examination of vehicles, victim’s injury, and details of the crime scene, the public’s doubt might be resolved. The circumstantial evidence was unique in nature.

Case Study 7 – In this case study10, the burned, dead body of a woman was found inside her house. The doors of the room were bolted from the inside, but the windows were open. Some tiles had been removed from the clay-tiled roof, and it was alleged that her husband set her on fire and escaped outside through the hole in the roof. Careful examination of the scene revealed that the hole in the clay-tiled roof was created after the fire ignited, and that the tiles were removed from the outside, not from the inside. This lead the investigation in the other direction. It was determined that the woman bolted herself in the room and took her own life while her husband desperately tried to save her by tearing a hole in the roof from outside. In this case, the unique pattern of pressure on the bamboo sticks on the roof of the house changed the direction of this investigation.

Case Study 8 – In this article, “Uniqueness: Concept at Scene of Crime,” we presented three case studies. These studies were purely part of the development of our concept on uniqueness of the crime scene11. This article became a milestone and the basis for our approach to the proposed theorem.

Theorem Of Uniqueness In Forensic Science
On the basis of our experiences and observations in the field of forensic science as reported above in Cases Studies 1–8, the theorem of uniqueness for forensic science is termed as: “Every crime scene has unique evidence even though the crime scene is similar in nature or modus operandi. The physical evidence, tool marks, and patterns must be unique in nature.”

Our statement will play an important role for the forensic expert while visiting crime scenes or while performing laboratory examinations, to find out the individuality or unique character of physical evidence, tool marks, and patterns. Therefore, the forensic community should develop an approach that searches for the unexpected within the crime scene.

Dr. Edmond Locard’s Exchange Principle might sound deceptively simple, but for almost a century it has been the fundamental axiom of crime scene investigation. This is the central guiding principle of forensic science. Trace evidence is a category of evidence that is characterized by materials that, because of their size or texture, are easily transferred from one location to another. In this sense, evidence is like pronouns in language: the thing itself is rarely examined sui generis, but rather bits of it that have transferred or something transferred to it that represent the thing (a noun, to extend the metaphor). Once transferred, they persist for some period of time until they are collected as evidence, lost through activities, or ignored. The analysis of trace evidence reveals associations between people, places, and things involved in criminal activity. The category “trace evidence and silent witness” encompasses a variety of materials, natural and manufactured, that require microscopy to identify and analyze. These materials include, but are not limited to, glass, soils, hairs, fibers, paint, pollen, wood, feathers, dust, and other detritus of things that surround us in our lives.

These days, forensic science is time-intensive and, above all, painstaking. Ask any experienced crime scene investigator and he or she will tell you that their two overriding watchwords are concentration and accuracy.

This is why it’s absolutely vital to make a visual record of the crime scene as soon as possible. As the renowned medical examiner Dr. Michael Baden puts it: “The first hour of a crime is critical.”12 The proposed “theorem of uniqueness” is an approach for the forensic community to trace out the exact, silent witness which is unique in each and every scene of crime. It is also suggested that the crime scene should be visited by the forensic expert as soon as possible.

About The Author
Dr. Mukesh Sharma is the Assistant Director of the Physics Division of the State Forensic Science Lab in Jaipur, Rajasthan, India, where he has visited 623 crime scenes and reported 600 cases. He is a qualified expert in physics (M.S.), material science (Ph.D.), and psychology (M.S.), with 12 years of experience in the field of forensic science and crime scene investigation. He has been awarded many times at the national and international level. Sharma has published more than 135 research articles and eight books in various fields of physics and forensic sciences.


1. James, S. H., J. J. Nordby, and S. Bell. 2009. Forensic Science: An Introduction to Scientific and Investigative Techniques, 3rd Ed., CRC Press, Boca Raton, FL.

2. Committee on Identifying the Needs of the Forensic Sciences Community, National Research Council. 2009. Strengthening Forensic Science in the United States: A Path Forward. NRC, Washington, DC.

3. Weston, N. 2009. Crime Scene to Court, The Essentials of Forensic Science, 2nd Ed. (ed. P.C. White), RSC, Cambridge.

4. Khajja, B. S., K. N. Vashistha, T. Bairwa, M. Sharma, S. Sharma, and G. K. Mathur. 2010. Trace evidence crack a suicide proved homicide: A case study. J Forensic Res. 1:103. Online

5. Sharma, M., B. S. Khajja, D. R. Godara, and G. K. Mathur. 2011. Alleged case of theft and murder unravel by forensic investigation. Forensic Magazine.

6. Kumar S., P. Jain, and M. Sharma. 2016. Importance of forensic investigation in explosion: A case study. J Forensic Res. 7:347. doi:10.4172/2157-7145.1000347

7. Jha, S. and M. Sharma. 2016. X-ray fluorescence Analysis: Useful for forensic examination. J Forensic Sci & Criminal Inves. 1(1):1–5.

8. Dixit, R., J. Surendra, P. Gupta, and M. Sharma. 2015. Unknowingly accident of fire: An expensive omission. J Forensic Res. 6:314. doi:10.4172/2157-7145.1000314

9. Sharma, M., S. Jha, and V. N. Mathur. 2011. What can an accident explain: A forensic case study. Indian J. of Forensic Medicine and Toxicology. 5:63–65.

10. Sharma, Mukesh, B. S. Khajja, Mayur Sharma, and S. Jha. 2011. Study of suspected burning case: A homicide or a suicide. J Forensic Res. 2:135.

11. Sharma, M. 2015. Uniqueness as concept of crime scene. Indian J. of Criminology and Crim. 34(1).

12. Baden, M., and M. Roach. 2001. New York: Simon & Schuster.

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The language barrier between English-speaking investigators and Spanish-speaking witnesses is a growing problem. (Updated 28 February 2011)