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Free «The Use of Biological Evidence in Criminal Investigations» Essay Sample


Biological fluids such as saliva, semen and blood, as well as human hair, have often been encountered and used as physical evidences in various instances of criminal investigations, such as robberies, sexual assaults (including rape), homicides and assaults. Saliva, semen and blood, due to their liquid properties, rapidly penetrate or coat the surfaces they come in contact with or are deposited on. As a result, when these fluids dry up, they cannot be easily removed, and at the same time, they cannot be easily seen with the naked eye. In addition, it is a well-known fact that, except for identical twins, no two persons are genetically identical. Therefore, the mentioned body fluids and human hairs are unique for every individual. This is why, a DNA examination of these biological fluids or their stains can help to attain a generic marker profile that is unique for every person (MCSO, par. 1- 2). This fact can help the criminal investigators a lot in identifying the suspects. Moreover, the above given information can also be used as evidence in such cases. This paper discusses the history of biological evidences, the reasons for their introduction and the methods of thir gathering and use in investigations. It will also discuss some individuals who were convicted or exonerated with the use of biological evidences.



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History of Biological Evidence

Biological evidence (often referred to as DNA evidence) had never been used until the mid 1980s. DNA fingerprinting (sometimes called DNA typing or DNA profiling) was originally described in 1985 by Dr. Alec Jeffreys, a geneticist from England. Jeffreys discovered that some regions of DNA consisted of DNA sequences, which recurred in a long pattern over and over again in close proximity to each other. In addition, the scientist also realized that the number of recurring sections observed in a sample varied from person to person. Jeffreys then developed a system that could be used to determine the DNA repeat sequences length variations (DNA Initiative, par. 2). As a result, he was able to carry out human identity tests by simply comparing DNA samples (FindLaw, par. 3).

The regions in the DNA that recurred were later known as variable number of tandem repeats (VNTRs). Dr. Jeffreys technique of examining the VNTRs is referred to as restriction fragment length polymorphism (RFLP). This name originated from the fact that the process involved the application of a particular restriction enzyme to divide the sections of DNA that surrounded the VNTRs. The first case that was solved using the RFLP technique was an immigration case in England. Therefore, the method was later successfully applied in a double homicide case. Its relative success in these two cases popularized its usage, not only in England, but also all over the world. Thus, human identity tests that use DNA profiling are still widespread nowadays (DNA Initiative, par. 3).  

During the past decade and a half, police officers and criminal laboratory workers have been witnessing a remarkable growth in the utilization of DNA evidence not only for criminal investigations, but also for paternity investigations. DNA evidence was first used in a United States court in 1988. Since then, its usage has greatly expanded. Nowadays, there are more than one hundred and fifty public forensic laboratories in the USA. Moreover, there are many private paternity examination laboratories in the country today. In total, hundreds of thousands of DNA related testing (for criminal investigation purposes or otherwise) are conducted every year in the US alone. Many other countries all over the world have forensic DNA programs. The permissibility and reliability of DNA evidence gives a reason to suppose that its use will only grow in the future. Therefore, more and more crimes that would have otherwise remained unresolved can be successfully investigated and their suspects identified, owing to the biological evidence (DNA Initiative, par. 3).

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Purpose of Biological Evidence

Biological evidence can be obtained from fluids such as saliva, semen, blood, and body structures such as hair, teeth and bones. Such evidence can be examined through DNA profiling that can lead to the identification of a specific individual they originated from. Biological evidence in criminal investigations has two main purposes. First, in cases where the suspect was allegedly found and is thus known, his/her DNA sample can be compared to the obtained biological evidence found at the scene where the crime was committed. The comparison results can be used to establish whether the suspect was indeed present at the crime scene or not. In case the results match, it may imply that the suspect may have committed the crime. Second, in cases where the suspect is not known, the biological evidence obtained from the scene of crime can be examined and compared to potential criminal offenders’ DNA samples contained in the existing DNA databases. This can help a lot in identifying the suspects. In the same way, the biological evidence can be used to connect many crime scenes (assuming that the perpetrator was the same). This simply means that biological evidence can be used to solve multiple mysterious crimes (James, pg. 5).

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From the above discussion, it can be said that the main purpose of biological evidence is to investigate crimes in which witness accounts are not sufficient enough or the witnesses are simply not there. This means that suspects can be found even if they were not seen or found in the act of committing a crime, as long as they left even a remote biological evidence. Thus, the use of biological evidence has facilitated criminal investigations. In addition, there are some cases that have been solved using biological evidence exclusively, since there were no witnesses of the crime. Such cases may have been unsolved, had DNA profiling not been discovered.

Gathering and Use

The condition, as well as location of any potential biological evidence has to be extensively documented before it is gathered and presented in court. Precise evidence documentation right at the scene of crime, at the autopsy room and finally at the forensic laboratory is extremely important. In all criminal investigations, documentation plays a leading role in determining whether the court will accept the biological evidence or not. For instance, the evidence can only be moved or processed after its original condition and all the relevant information has been rightfully documented (Lee & Ladd, pg. 3). There are several ways of documenting the biological evidences as outlined below.

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At the crime scene, the evidence is photographed or videotaped (or both) prior to touching, moving and gathering. Its condition and location relative to the crime scene is also recorded. Other relevant objects in the crime scene are also noted down. The evidence is then carefully gathered (with no tampering or other actions that may distort the evidence) into a package that is initialized, labeled and sealed (Lee & Land, pg. 4).

At the forensic laboratory, the received package is again labeled (for the laboratory references) and the seal condition is noted. The forensic personnel have to ensure that the package corresponds to the case number and that all the information (date, time, submitter’s name, agency, contents, inventories etc) is recorded properly. They also have to confirm that the descriptions provided are real. Next, they have to authenticate the evidence. The testing procedures, quantity of samples used and the results also have to be recorded. It is forensic personnel’s duty to ensure that the evidence is not tampered with by observing all clinical procedures (Lee & Ladd, pg. 4).

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The ability of biological evidence to be presented and accepted in a court of law is also influenced greatly by the gathering process and subsequent preservation methods. The integrity of the evidence, whether legal or scientific, starts from the initial investigation at the scene of crime. There are various evidence collection protocols that have since been established by the authoritative bodies. However, there is no universal method that can be used in all the cases, since the condition and state of the biological evidence vary from case to case and thus require different collection techniques. Nevertheless, there are some general principles that need to be followed. For instance, a significant quantity of evidence should be gathered sor a sufficient DNA to be found for testing purposes. In addition, certain materials from the surrounding area (such as non-biological fluids, grease and dirt) have to be avoided or limited at the time of collection since they may affect the DNA profiling (Lee & Ladd, pg. 3).

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As mentioned earlier in this paper, the biological evidence has to be packed in line with conventional forensic practices. Once gathered, the evidence has to be taken to the forensic laboratory as promptly as possible. Proper testing and preservation procedures have to be followed, so that the evidence is not tampered with (Lee & Ladd, pg. 3). If the criminal investigators gather the biological evidence and handle it properly, and if the forensic scientists apply the established procedures (and of course carry out the DNA analysis correctly), the DNA evidence can be exceptionally accurate. The probability of one person’s DNA profile matching that of someone else is very small (1:1,000,000,000). Considering that eyewitness testimony and fingerprinting can be flawed or inaccurate, biological evidence is so far the most reliable way of matching a suspect to the biological samples gathered during the investigation. As a result, the courts can rely on them when passing the judgment (FindLaw, par. 7- 8).

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Crimes Solved Using Biological Evidence

In 1997, a mysterious murder case in King County was solved when the biological evidence obtained from the crime scene matched the DNA sample of a previously convicted sex offender. In Arizona, a rape case of 1993 that had gone unresolved was finally solved when DNA samples from a man who was only convicted two years later in Washington matched the evidence at the rape scene. Similarly, in 1999, a man in New York was successfully linked to more than 22 robberies and sexual assaults with the help of the DNA evidence. In 2002, criminal investigators used biological evidence to link a man to a series of rapes and murders in Pennsylvania, Colorado, Fort Collins and Philadelphia. In addition, the world known Green River killings that were staying unresolved for many years despite consuming more than $15 millions of investigation expenses and a huge investigation forces were only solved via biological evidence.  At the same time, evidence from a rape in Phoenix matched the DNA from a Tacoma rape and these samples were successfully matched to a convicted felon in Arizona. These are only some of the numerous cases solved using biological evidence (Digital Archives, par. 1- 2; Department of Justice, par. 2).

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There have also been some people who had been convicted erroneously and have thus been exonerated after the examination of biological evidence. For instance, Cornelius Dupree was sentenced for 75 years in 1980, after it was alleged that he had raped and robbed a woman in Dallas, However, later the DNA evidence proved that it was actually another man who had committed the offence. By the time of his release last year, Dupree had served 30 years and was entitled to $2.4 million compensation (Richards, par. 2-4). A similar case happened recently, when a man in Colorado was also exonerated from his sentence. In general, there have been about 300 exonerations (most of which applied to those convicted of rape or murder) since 1989 when DNA evidence came into use. About 17 of the convicts were to face the death penalty. This simply means that the use of biological evidence has saved many people whose lives had been shattered by the previous erroneous eyewitness accounts (ACLU, par. 1).


The advancement of biological evidence and DNA profiling is very helpful for crimes investigations. When the evidence is handled and gathered properly, it can be used to solve many crimines due to its unique accuracy. At the moment, many defense lawyers do not challenge the DNA results; rather, they challenge any mishandling of the evidence to discredit. This underlines the importance of the biological evidence for criminal investigations.


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