The Scientific Method Applied to Forensic Science

Table of Content


Forensic science is a field of endeavor where the fundamental techniques and principles in the basic sciences like in Chemistry, Biology, and Physics are all integrated to facilitate the search for a logical solution for various crimes (Inman and Rudin, 2000). Forensic scientists patiently work hand-in-hand with the crime specialists, law personnel, prosecutors, investigating group, and defense attorneys in order to present the truth before the trial court, as revealed by the crime evidences. They employ scientific method in the gathering of factual evidences which serve as an important basis of a sound decision for the juror’s verdict.

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Since forensic science is anchored on science disciplines and scientific method, it is open then to any challenge with respect to the validity or reliability of its principle, validated hypotheses, and theories (Siegel, 2006). Thus, a witness’ testimony based on a scientific technique or theory is insufficient to prove its veracity. The testimony or physical evidence can be presented and accepted before the trial court but the veracity of such is stipulated until such time that an independent panel has examined its validity and reliability (Siegel, 2006). As such, the testimony of an expert in a particular field of endeavor should be scrutinized not only based on his or her field of specialization but also in the perspectives of every science disciplines. In particular, during cross-examination, the assessment on the concurrence of a witness’ testimony or physical evidence on scientific method and scientific knowledge as well as on the other forensic science-allied disciplines is done (Siegel, 2006).

Observation and description of a phenomenon or a group of phenomena

In the crime scenes, forensic experts gather and document physical evidences, and cautiously handle such for laboratory analysis and interpretation (Inman and Rudin, 2000). Upon collecting evidences, the crime scene is demarcated, photographed, and sketched. Also, the crime scene investigators eliminate the other materials in the area which have no direct bearing with the case; thus, they must posses a sharp discretion as to what materials in the scene must be treated as crucial evidence or else probative evidence will be missed. Then, every item found in the marked area is separately packed and documented with the time, location, and date of collection. Each item must properly be handled so as to avoid the possible contamination and to preserve its authenticity.

Prior to the laboratory analysis of an item, the forensic expert must understand the aim of the defense or prosecutor in requesting for the experimental testing (Fisher, 200). For instance, if the prosecutor requested for the possible presence of an illegal drug in an item, the analyst must consider the legal definition, classification, and illegal dosage of a particular substance based on the relevant statute. For example, if the law defined the possession of cocaine in the form of salt and the cocaine base separately, the analyst then must employ analytical procedure that detects the presence of cocaine in these forms separately.

Performance of experimental tests of the predictions by several independent experimenters

After the determination of the valid evidences, a sample material from each will be taken and subjected to the laboratory tests. For example, in obtaining a sample from dried blood on a floor tile, a moistened swap will be used to collect from the dried blood and another swab to the blood adjacent to the location of the first collected dried blood (Inman and Rudin, 2000). Since the laboratory analysis of samples requires both positive and negative controls, the second swabbing is done to serve as a substrate control. In particular, several positive and negative controls are typically made during the laboratory analysis to validate the expected observation for both positive and negative controls (Lee, Palmbach, and Miller, 2001). In such way, one can qualitatively discern the accuracy of the laboratory testing.

As the collected materials reach the laboratory, they are properly documented once more to assure the chain of custody, then stored until such time that a final decision concerning the standard analytical procedures which a specific material shall undergo has made. For instance, in a bloody fingerprint case, the blood must undergo laboratory testing while the fingerprint must be preserved through documentation. The DNA experts and the serologists must work with the finger print experts in order to extract the details of the possible information embedded in such material evidence which may shed light on the event happened during the crime. This is the process of crime reconstruction (Lee, Palmbach, and Miller, 2001).

Meanwhile, different experts can possibly interpret the results of the analysis in different ways. In order to validate the results of the analysis, the defense can make a request for an independent laboratory testing of the material evidence involved. If the collection of evidence is done in two swabs, one must be allotted for the defense or if possible, the defense counsel shall be summoned to witness the laboratory testing and analysis of such evidence. Hence, the forensic expert is expected to be impartial and objective in the conduct of laboratory analyses for the involved evidences.

Formulation of a hypothesis or hypotheses to explain the phenomena

Forensic scientists are not only concerned on the technical analysis of a physical evidence but also on the proper handling, chain of custody, and preservation of the item as well as on the report preparation and testimony of such before the trial court (Fisher, 200). In addition, in every stage of the analysis of physical evidence, the forensic expert must conform with legal requirements in order to ensure that in the end of analysis the results will definitely admissible to the trial court. In testifying in the trial court, the forensic expert needs to present the high technicality of the analytical procedures and instrumentation along with the results and their corresponding implication on the committed crime in a manner that could be easily appreciated by every individual in the court.

In crime reconstruction, hypothesis is formulated after the traces of an action have been examined (Chisum, 2006). On the contrary, in science disciplines, the phenomena are observed prior to the formulation of hypotheses. Scientists formulate hypotheses about the phenomena and subject those into experimental tests. If the experimental results contradicted the notions of the tested hypotheses, formulation and experimental testing of hypotheses will again be done until such time the results of the experiments can plausibly explain the occurrence of the phenomena. Then, the tested hypothesis which resulted to experimental data and supported the occurrence of a phenomenon becomes a validated hypothesis. In the same manner, the scientific method is employed in crime reconstruction (Chisum, 2006). The formulation of hypotheses on the cause of a certain crime is done, and then each hypothesis is tested against the collected material evidences through the laboratory analysis. If the experimental results for specific evidence are in contrary to the notion of a hypothesis, the hypothesis is rejected and another formulated hypothesis is subjected into experimental testing. As such, the forensic scientist must create an experimental design specific to the type of physical evidence to be examined.

Use of the hypothesis to predict the existence of other phenomena, or to predict quantitatively the results of new observations

The actions that have previously occurred and the positions of the individuals involved in a crime are logically inferred based on the accuracy of the assessment done on the physical evidences (Fridell, 2007). As well, the functional condition of the material evidence sheds light on the possible events that have taken place. For example, a wall clock hit by a strayed bullet would stop and illuminate the time in which the gun was fired. Thus, forensic experts should seek ways to find out the prior events based on the physical evidence on the crime scene. The proper documentation then, through sketches and photographs, of the material evidences in tandem with the accuracy of the experimental testing and laboratory analysis has a crucial role in solving a crime (Fridell, 2007). These evidences provide cues for the establishment of sequence of events occurred in a crime case. For instance, the bloody footprints from the crime scene can lead the investigators to the path taken by the culprit after committing the crime.

Forensic examinations are intended either for comparison or identification (Houck, 2001).   In identification cases, specific chemical species like the amount of antimony and barium in gunshot residues, the amount of alcohol in blood, and the presence of illegal drugs in tissues is determined and quantified. In line with this, specific analytical procedures for physical evidence should be designed to guarantee accurate results which in turn become the bases of comparison or identification (Houck, 2001). In the laboratory test for an illegal drug, for instance, involves a series of laboratory tests specific to the identification and quantification of the suspected drug. Then, a sufficient sample of the material is subjected into several colorometric tests to determine the presence of illegal substance. When the tests yielded a positive result, the identity of the substance will be examined. Then, another sample of the item will undergo extraction and chromatography in order to separate its components. Next, through spectroscopy and gas chromatography, the substance’s identity and quantity are respectively determined.

The comparative assessment, on the other hand, reveals the inconsistencies or concurrence between the properties of two samples in proving whether or not they originated from a single source. Since industrial products are manufactured in large batches, most materials have homogeneous characteristics (Houck, 2001). In particular, paints are manufactured in thousands of gallons; thus, it is possible that a sample of paint from one car is identical to a sample from another car especially when both of these cars were manufactured by the same company. In connection to this, in a hit-and-run vehicular accident, the paint of the car is often transferred into the victim’s body (Houck, 2001). The paint residue is subjected into laboratory analysis to determine its properties such as pigments and composition. The results of this analysis are then matched to the laboratory test results of the paint sample from the car of the suspected villain. The result comparison will reveal the inconsistencies or prove the common origin of the two samples examined.

As similar to the application of scientific method to scientific disciplines, the predicted solutions for a crime case must be logically supported by the empirical results of the laboratory experiments. Invalidated proofs and super natural causes like aliens and spirits are not considered in a systematic crime examination (Chisum, 2006). In science, only a single hypothesis should be proven as a cause of a phenomenon; thus, the alternatives are rejected and considered as falsehoods. Since “falsification” is the backbone of the scientific method, in crime reconstruction, the expert formulates hypotheses which in turn she or he attempt to disprove. After the experimentation, the forensic expert can now declare that a particular hypothesis is not supported by the examination done to the submitted evidence (Chisum, 2006).


Chisum, J.W. (2006). Crime Reconstruction. Mozayani, A. and Noziglia, C. Eds. The Forensic Laboratory Handbook: Procedures and Practice. Totowa, New Jersey: Humana Press.

Fisher, B.A. (2000). Techniques of Crime Scene Investigation. Boca Raton, FL: CRC Press.

Fridell, R. (2007). Forensic science. Cool science. Minneapolis, Minn: Lerner Publications.

Houck, M.M. (2001). Mute Witnesses: Trace Evidence Analysis. San Diego, CA: Academic Press.

Inman, K., and Rudin, N. (2000) Principles and Practice of Criminalistics. Boca Raton, Florida: CRC.

Lee, H., Palmbach, T. M., and Miller, M. T. (2001) Henry Lee’s crime Scene Handbook. New York: Academic Press.

Siegel, J.A. (2006). Forensic Science: The Basics.  Boca Raton, FL: CRC Press.


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