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October 02, 2018 Also in this Issue

Forensic Science : A Forensic Scientist’s Perspective

By David San Pietro, PhD and Brooke W. Kammrath, PhD

What is forensic science? Often, we define our field as “the natural sciences applied to matters of the law,” but it is more than this. At its foundation, there are several concepts that distinguish it from other scientific areas, thus making forensic science more than simply an amalgam of the established sciences (e.g., chemistry, biology, physics). Forensic science has a rich history, with many people contributing to its status as its own scientific discipline. These defining concepts include Paul Kirk’s principle of individualization as well as Edmond Locard’s exchange principle (“every contact leaves a trace”). Since the early days of the field’s development, forensic scientists were responsible for not only interfacing with items of evidence on a chemical and physical level, but also with all aspects of physical evidence from initial recognition at the scene through its analysis and interpretation of significance. Unfortunately, we have deviated from this model and narrowed the scope of our activities.

In Professor Peter De Forest’s 1997 Founders’ Lecture to the California Association of Criminalists, he asked whether or not the field of forensic science has advanced given the rapid growth of technology. He stated:

On the face of it there would seem to be no question that the field of criminalistics has advanced. But has it? While we have forged ahead technologically, in my view we have backslid with respect to our core activity—that of applying science and scientific reasoning to criminal and civil investigations. We should take care not to confuse the tools with the essence of the enterprise.1

Regrettably, we agree with Dr. De Forest and fear that in the nearly twenty years since this lecture and subsequent publication, things have only continued to decline. So why should this be of concern to those beyond the field of forensics, such as to members of the legal profession? Simply stated, the diminishment of the forensic scientist leads to poorer forensic science services. This can negatively impact cases via the generation of nonrelevant information, wasted resources, the introduction of investigative “red herrings,” and overlooked, neglected, or irrevocably altered evidence. All of this ultimately reduces the capabilities of forensic evidence and can inhibit the appropriate resolution of a case.

What did Dr. De Forest mean by backslid? What is the current state of forensic science and how does it deviate from its original scope? We as forensic scientists regrettably have abdicated our scientific roles on both the front and back ends of case investigations.

On the front end, we have contributed to the reduction of our role at the crime scene, with the resultant loss of scientific inquiry at the scene. Additionally, this has adverse implications for the laboratory where forensic scientists are no longer responsible for directing the analysis of an item of evidence submitted to the laboratory. This has resulted in nonscientists filling the void, thus framing and formulating scientific questions that should be posed by forensic scientists. Paradoxically, the fire science community has recently recognized the value of having scientists investigate fire scenes2 while the need for scientists at crime scenes has become critically unappreciated and suffers from a lack of awareness by the criminal justice community.

Additionally, at the back end, we continue to allow the interpretation of the significance of evidence to be performed by nonscientist law enforcement personnel or attorneys who are free to impart their own bias onto its interpretation. This is humorously exemplified in the movie My Cousin Vinny, where the prosecuting attorney declares two tire tread materials “identical” with a clap of his hands, thus imparting misleading significance onto the evidence, which were simply mass-manufactured tires. This issue exists not only in the cinematic universe, but also in real courtrooms. One of the present authors was asked to provide testimony regarding the significance of DNA results of the swabbing of a firearm. The evidence was submitted to investigate the possibility of contact between the suspect and the weapon. The nature of the results was such that there was a “match” at two loci within the mixture profile generated. In lieu of weak statistical results (one in seventy-eight), the prosecutor was enthusiastic to present her interpretation of “matching” evidence to the jury even though there was limited value to this scientific result, thus shaping it to meet the probative needs of the case. To ensure the interpretation of the evidence was conveyed appropriately and without bias, this forensic scientist made sure to accurately explain its significance (the approximate equivalent of four people out of three hundred who could have been contributors to this evidence). This illustrates the possible misrepresentation of evidence significance often encountered and the need for the forensic scientist to take ownership of the evidence interpretation and how it is presented to the triers of fact.

Lamentably, what we appear to have done, consciously or not, is to step away from our previous roles regarding the application of scientific reasoning to the forensic endeavor. As it is known that nature abhors a vacuum, once the niche was vacated, others (i.e., nonscientific personnel) were more than willing to step in and fill the scientific void. There are three primary areas of this void to be considered and discussed further.

Respect of the Forensic Science Expert’s Expertise

Oftentimes the clinical laboratory is cited as a model for how forensic science laboratories should be structured. Although this may seem logical, it is forgotten that in the medical clinical laboratory, the physicians are the ones who are ordering the tests and analyses. This makes perfect sense for the proper diagnosis and treatment of various conditions. However, in the field of forensic science this model has fundamental flaws. Primarily, it is the abdication of the analytical decision making to nonscientific personnel. Often, this is in the form of police detectives, case investigators, or attorneys. This is inherently wrong, as it is akin to having a medical patient ordering the diagnostic tests, evaluating the results, and determining treatment.

As forensic science practitioners, we have been scientifically educated and trained to recognize, evaluate, and reconstruct physical evidence. This is no different than the experience often relied upon by physicians in a clinical environment, which is used to recognize, diagnose, and treat medical cases. It is absurd to think of a patient performing a self-examination and self-diagnosis (despite the recent availability of Dr. Google), yet it is commonplace for forensic science investigations to be directed by nonscientists. It is our assertion that this has serious adverse implications for casework investigations.

Forensic scientists specifically bring education, training, and experience, which, when combined with a rigorous adherence to the scientific method, provide a problem-solving approach to case investigations. Although using the scientific method may seem trivial, especially considering it is outlined in every middle school science course, we must consciously strive for its proper application. Forensic scientists are educated to use these scientifically derived data to try to falsify an initial hypothesis. While destruction of hypotheses seems counterintuitive to many, it is the basis for a truly unbiased attempt at a reconstruction of an event. Rigid observance of the steps of the scientific method ensures that the hypothesis fits the evidence and not the other way around.3 In addition, by incorporating data rigorously obtained through the scientific method, when viewed through the appropriate contextual prism of the case, forensic scientists can critically ask the appropriate questions and unbiasedly influence the possible direction of the investigation.

All too often, the expertise of the forensic scientist, as described above, is not appreciated, recognized, or utilized. We often are relegated to taking our marching orders from law enforcement and legal personnel. What this sometimes leads to is the scientific misdirection of cases and the missed opportunities to answer overlooked or unrecognized questions with the physical evidence that could provide a quicker or more accurate resolution.

On a grander scale, forensic scientists were minimally involved with the recent President’s Council of Advisors on Science and Technology (PCAST) report related to the validity of our field of expertise.4 Instead, the Council was composed of nonforensic scientists who consulted numerous legal professionals (attorneys, law professors, and judges). Although a few forensic scientists were asked to answer questions from the Council, their contributions were minimal. What resulted was not only a skewed view of our functions, but an extremely incorrect one. Consequently, it has been lambasted by numerous professional organizations, both legal and forensic.

Deterioration of Scientific Reasoning and Critical Thinking

Unfortunately, one consequence of a nonscientific-led inquiry is the “shotgun” approach to physical evidence. This is characterized by the absence of any form of critical thinking in regards to the recognition and collection of physical evidence, whose relevance should be defined in the context of the scene. Frequently, it has been overheard, “Collect it all and let the lab sort it out.” This has huge negative implications both at the scene and in the laboratory. In both instances, this creates an extreme waste of resources: time, man-hours, and consumables. More importantly, it can lead to crucial inculpatory or exculpatory evidence going unrecognized and consequently being undeveloped. Having scientifically educated and trained forensic scientists at a crime scene effectively applying the scientific method enables the reconstruction of events and collection of probative evidence items. This minimizes the potential for missing nonobvious items or destroying critical evidence. Additionally, in the laboratory there is usually the expectation by the investigators that all submitted evidence items are analyzed. By analyzing all items without any context concerning the scene and physical evidence, one runs the risk of generating extraneous and irrelevant information that distracts from or misdirects the investigation.

A case example can help illustrate several of these issues. In a stabbing murder investigation, a request was made to the forensic laboratory for the DNA analysis of a bloodstain on the pants of the suspect. The laboratory technician was provided with no contextual information and performed only a cursory documentation of the initial stain by cutting the sample (i.e., destroying it) for DNA analysis. As a result, later questions regarding the possible mechanism of blood deposition could not be adequately answered from the photographs or laboratory bench notes provided. Whether the blood was the result of a contact transfer or spatter event was of critical importance but could not be determined. The absence of critical thinking on the part of both the evidence submitter and the technician, coupled with an obvious lack of holistic awareness of other evidence forms (i.e., bloodstain patterns), can be said to have doomed this endeavor from the start. Here is a situation where misdirected focus toward the DNA results/statistics power of discrimination took away from the probative question of how this stain was deposited. Regardless of the size or power of the DNA statistic, it sheds absolutely no light on this particular question, thus hindering a timely, meaningful case resolution.

Diminution of the Role of the Forensic Scientist

Paul Kirk was instrumental in defining forensic science as a profession and the great potential role of the forensic scientist in crime investigation (Kirk, 1963a; Kirk, 1963b).5 He wrote:

Just as the skill of the doctor does not rest on the excellence of his stethoscope or the sharpness of his scalpel, the excellence of the criminalist does not depend on the multiplicity of his instruments. A master of all techniques may remain merely a technician, and the best of all technicians is not necessarily a satisfactory criminalist. The criminalist must analyze the problem and understand the principle in order to arrive at a correct interpretation of the criminal act. In addition, he must be second to none in objectivity, for on his objectivity may depend the lives and liberties of other people. These obvious facts bear repeating only because they are often disregarded.6

As Kirk asserts, although advancements in new technologies are always desirable and often beneficial, they are less important than fostering scientific reasoning. In effect, we have focused more on the forensic equivalents of the stethoscope and scalpel (i.e., the DNA genetic analyzer or mass spectrometer) rather than encouraging a holistic approach to investigations. The intellectual and training investments required to master new technologies have led to increased specialization. While we do not dispute the need for specialization, we cannot allow it to substitute for forensic scientific reasoning.

Referencing the stabbing murder case example previously discussed, we see an example of what has been referred to by Peter De Forest as the result of a reactive forensic laboratory approach, where any scientific questions are circumscribed by the submitters and examined by technicians in a production-line mentality as per the request of the nonscientist.7 This reduces the potential value of the possible physical evidence and, in that case, resulted in unanswered questions that could easily have been resolved had the right questions been asked at the investigation’s onset. This leads to our next point.

Because the previously cited shortcomings of our field are in part due to increased specialization, we have unwittingly created a culture of forensic science technicians at the expense of scientists. For example, some DNA analysts consider themselves that and nothing more; thus, they are not equipped to recognize or evaluate or are not sufficiently interested in other potential forms of evidence they may encounter, such as bloodstain patterns and trace evidence. In our opinion, this underscores the need for a generalist practitioner. We want to be clear that the generalist cannot be seen as a “jack of all trades, master of none,” but rather a scientist with a broad scientific knowledge and the ability to maximize evidence potential through a keen aptitude for scientific recognition and a deep understanding of how the different types of physical evidence can work together to contribute to the solution of a case. It is our view that the structuring of forensic facilities has regrettably taken on more of an assembly-line mentality that uses limited and stringently controlled approaches to address predefined questions to process the large number of items submitted. Although this is appropriate work for some areas, such as street drug analysis, it presents a limited scope in terms of both the analysis of case evidence and the development of the forensic analysts’ holistic acuity. This unfortunately manifests itself as a lack of opportunity for the growth of proactive forensic scientists in favor of the growth of reactive forensic technicians. The inherent risk of this is forensic scientists from different disciplines operating in a vacuum with little case continuity or connection, thus preventing a complete and cohesive reconstruction of an event from the physical evidence. This represents two related ideas: the systematic obfuscation of complex case solutions and the inexorable drift from scientist to technician. The potential implications of this should be obvious, but unfortunately may not be. The power of physical evidence to reveal the ground truth about the events in question should be neither undervalued nor unrecognized.


Given the points we have discussed, we see this as the decline of the existence of forensic science as we know it.8 Presently, we perceive the harbinger of this as more than just the elimination of certain forensic specialties (i.e., trace and pattern evidence) from state and local laboratories, but in the deficiency of education regarding the fundamental forensic science concepts and principles. Clearly there has developed a crack in the forensic science foundation, which, left unattended, stands to see the whole structure come crumbling down. It is not too late to reverse course and recapture the essence of forensic science as envisioned by our pioneers and mentors.

Earlier we asked, Why should attorneys care about the decline of forensic science? Hopefully we have adequately addressed this issue. Now the question becomes what can attorneys do to help forensic scientists maximize the potential of our field? As we discussed, the first step is to recognize the scientific expertise and underutilized abilities in both the front and back ends of an investigation. This can be translated into action through fostering the collaboration between scientists and law enforcement investigators at the crime scene as well as the laboratory. Simply put, it requires a willingness to allow for the application of scientific reasoning at all stages of a case investigation. In the same way that forensic scientists would not be involved in dictating or advising on legal issues, nor should the nonscientist be directing the scientific inquiries. Lastly, forensic scientists and members of the legal community should always strive for open communication. It is only through this that forensic science can maximize its contribution to develop both inculpatory and exculpatory physical evidence, and thus most effectively assist the triers of fact in reaching their goals.


We are indebted to the mentorship of Professor Peter De Forest, and greatly appreciate his thoughtful review and constructive comments of this manuscript.


1. P.R. De Forest, Founders Lecture, Recapturing the Essence of Criminalistics, 39(3) Sci. & Just. 196c208 (1999).

2. J.J. Lentini, What Fire Litigators Need to Know in 2017 13(4) SciTech Lawyer 18–21, 31 (2017).

3. De Forest, supra note 1.

4. President’s Council of Advisors on Sci. & Tech., Exec. Office of the President, Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods (Sept. 2016),

5. P.L. Kirk, Criminalistics, 140 Sci. 367–370 (1963); P.L. Kirk, The Ontogeny of Criminalistics, 54 J. Crim. L., Criminology & Police Sci. 235–238 (1963).

6. Kirk, Criminalistics, supra note 5, at 368.

7. De Forest, supra note 1.

8. Claude Roux et al., The End of the (Forensic Science) World as We Know It? The Example of Trace Evidence, 370 Phil. Transactions Royal Soc’y B 20140260 (2015),

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By David San Pietro, PhD and Brooke W. Kammrath, PhD

Dr. David San Pietro ([email protected]) and Dr. Brooke W. Kammrath ([email protected]) are Associate Professors in the Forensic Science Department of the Henry C. Lee College of Criminal Justice and Forensic Sciences in West Haven, Connecticut.