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Forensic Science: Term Definition Research Paper

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Updated: Oct 2nd, 2021

In the past decade, forensic science has become a powerful field due to its significance as supporting evidence in criminal cases. The development of handling and analysis techniques of DNA samples has led forensic investigators to rely on the information forensic science can offer. The combination of DNA analysis with the study of surrounding insects (entomology) and pollen (palynology) has resulted in an efficient and effective method in investigating criminal cases (Leclair et al., 2004). The inclusion of forensic data in criminal investigations has thus transformed the process of conviction and to a certain extent, has overturned particular verdicts upon review of old cases. Unfortunately, in many cases the convicted individual is usually sentenced to death and the DNA evidence is too late to overturn the sentence.

The significant upgrades in the field of information technology have also enhanced the capabilities of criminal investigation to solve old cases. These cases that have occurred in the past, ranging from a few years to decades, are technically referred to as cold cases. The computerization of criminal records has generated a powerful database tool, making the activity of checking old files easier and more efficient. Currently, every local police department employs a database that is networked to both state and national databases for a quick reference. CODIS is a two-part DNA database that is currently maintained in police departments—one serves as a catalog of criminal cases, while the other database contains files of missing persons. The path of criminal case investigation to date is initiated by generating a DNA profile based on what is collected at the crime scene. This particular DNA profile, linked to the rest of the databases in the network, will search for similarities in DNA profiles previously submitted to the database. Should there be a match, the criminal linked to that particular DNA profile will be pulled out and the investigation proceeds to the next step. Such automated method of searching for matches with existing records in the databases saves a significant amount of time. However, it should be understood that the chances of finding a match in the database depends on the number of DNA samples that were collected in different crime scenes through the years. It is also important that a DNA profile has been generated from every DNA sample that was collected from the crime scene.

In the case of missing persons, a DNA profile database will be helpful in identifying bodies that have been recovered and are difficult to recognize in terms of facial features. Such obstacles of unidentifiable human remains are often observed among cold cases due to the degree of composition of the human body over time. In an extreme case, the remains of a person may consist of only bones and a few tissue parts, hence the employment of DNA isolation and profiling will definitely be helpful in identifying the body. The same conditions could be applicable to incidents such as fires, explosions and plane crashes, wherein there is much deterioration of human flesh and it is difficult to identify a body based mainly on physical features.

It should be noted that the development of DNA profile databases not only makes the retrieval of criminal information simpler and faster, such computerized file systems may also lower the crime rate. The positive identification of DNA samples have led to higher conviction rates thus reducing the possibility of future criminal acts of these individuals. DNA profiles are very unique in that it does not generate false positive matches. The system of DNA sequencing identifies the number of nucleotide bases that are unique to each individual and can only occur at a specific sequence and a number of repeats,, distinguishing bodies belonging to relatives and which body belongs to the mother, the father, and the child.

The power of DNA profiling can be employed on cold cases because it allows the isolation of DNA from old evidences that may contain biological samples that are associated with the crime, including old blood stains, saliva, hair and skin. The DNA molecule is extremely stable because it can withstand years unchanged as long as it is not exposed to fire and/or acid. In the case of fire crime scenes, DNA can still be isolated from the inner area of the teeth, or the enamel, which is protected from heat by the surrounding tooth structure.

Forensic crime scene investigation currently employs the study of human remains and this also involves extraction of DNA from the tissues for inclusion in the polymerase chain reaction, which is an enzymatic amplification of specific DNA sequences of a particular DNA sample, be it the victim, the suspect or any other individual in the crime scene, through a series of varying temperatures in order to generate sample-specific DNA patterns that are visualized on an electrophoretic gel. The specific DNA sequences employed in forensic DNA analysis are known as short tandem repeats (STRs), which are present across the entire genome of each individual. The power of STR analysis is based on the premise that each individual carries a unique STR pattern that can distinguish one person from another, just the same as how fingerprinting works. Forensic DNA analysis is more reliable than fingerprinting because DNA can never be erased or changed, unlike fingerprints which could be removed when the fingers of a suspect are burned or are covered by gloves, resulting in fingerprint-free hands. The principle of STR analysis comes from the concept that these DNA sequences have a unique number of copies in each individual and the probability of having two individuals having the same number of copies exponentially decreases as more DNA locations or loci are analyzed.

Results from the STR analysis of forensic DNA samples may show either the same or different DNA profile between the suspect’s actual DNA and the DNA collected from the crime scene. These sentences in blue do not make sense. If the results show a different DNA profile from that of the DNA collected from the crime scene, then the suspect can be indicted from the criminal investigation. However, if the DNA profile from the STR analysis is similar, then the suspect can convicted immediately. The forensic scientist must then compute for the probability that an individual picked out through a random process would general an identical profile as that employed in the STR analysis. The principle of population genetics is the core behind this computation, which involves a combination of statistics, mathematics, genetics and biology. The Hardy-Weinberg Law of Equilibrium is applied to cases that show positive results in the STR analysis. This determines the chances that an individual selected at random would have a similar DNA profile with those STR sequences which were analyzed (Cash et al., 2003). Each STR sequence is treated as a genotype or a genetic combination, which is specific to each DNA region in the human genome. Hence, when determining the probability of having an individual with the same DNA profile for 10 genotypes, the product of all the genotype frequencies should be calculated.

Though forensic DNA analysis is very powerful and reliable, this method is also subject to human error which could then result in incorrect convictions. The employment of forensic DNA analysis is very critical in cases wherein no other supporting evidence can be collected from the crime scene, the victim, or the suspect. Errors in handling forensic DNA may include contamination, wherein the samples employed in the analysis contains a mixture of more than one biological organism, which may be either another individual different from the actual analyzed person, as well as DNA from bacteria that may be present at the site of collection. Another error in handling forensic DNA samples may also involve degradation of the sample, which pertains to the breakage of the DNA in the samples collected (Coble and Butler, 2005). Intact DNA is necessary when performing STR analysis and degradation of DNA could result from exposure of the collected samples to heat or reagents such as acid, bleach, alcohol or preservatives such as formalin or acetone. Heat associated in a crime scene may be due to a fire or burning of only a particular part of the crime scene where the collected sample was situated. Intact DNA is essential for the success of an STR analysis because the STR sequences have to be located in the entire genome of an individual. Any breakages in the genome would result in an erroneous result in the analysis wherein either an STR region may not be identified because that particular region could not detected because it was probably located in an area that was degraded. It should be understood that although forensic DNA analysis requires specific conditions for sample collection and DNA handling, the procedure is very reliable and robust that even samples that have been stored in a preservative or alcohol for decades or centuries may be employed as source of DNA for STR analysis.

In order to prevent contamination of samples that will be used for forensic analysis, quality-control procedures have been designed in order to have a standardized method of conducting the collection and handling of material. The use of protective wear such as gloves, face masks and laboratory gowns are necessary in handing forensic samples. In addition, structural equipment such as HEPA-filtered air duct systems, biological hoods, and sanitized rooms are also necessary to ensure that contamination does not occur during the analysis. The systematic labeling and recording of forensic samples and DNA material are also important in the success of DNA analysis. It is easier for the forensic scientist to rule out any problems with contamination and just focus on analyzing any similarities in the DNA profiles of the individuals being investigated in the forensic laboratory.

Aside from employing forensic DNA analysis in crime investigations, STR analysis may also be employed in the identification of victims in mass fatalities or disasters such as bombings, tsunamis, plane crashes and mass graveyards (Budimlija et al., 2003). In such conditions, wherein not only two individuals (victim and suspect) are involved, a more tedious process of collection, handling and analysis of DNA samples is conducted. Forensic DNA analysis of victims in a mass disaster needs reference samples which actually pertain to material facilitating the positive identification of a body. Two kinds of reference samples are generally employed in this type of forensic analysis. The DNA samples collected from the victim’s family members are employed as a reference sample. Personal effects of a victim are also employed as reference samples such as biological specimens that may have been collected before death or antemortem, biopsies from the hospital in which the victim may have gone to for medical consultation, or bloodstain cards of the victim that may be been issued during a biomedical test. Simple antemortem reference samples are also admissible for forensic analysis and these may include toothbrushes, razors, and shavers. However, these reference samples may generate errors in the analysis because these items may also be contaminated with DNA from other individuals or other biological organisms. If contamination is present in these reference samples, the positive identification of a victim’s body may fail or may result in mixed DNA profiles, which in turn will lead to a confusing identification. Another way to further strengthen the positive result generated from an antemortem reference sample is to analyze a family member or a second antemortem reference sample. It is thus important that kinship analysis be performed to further strengthen the results obtained when using antemortem reference samples. These reference samples are generally more reliable than personal items such as toothbrushes and razors.

When conducting DNA profile assays, it is important that a significant number of STR patterns are analyzed (Alonso et al., 2005). It has been determined that analyzing 13 to 17 STR patterns generate more reliable results in DNA analysis so that the DNA profiles collected will show more discriminatory power in terms positively identifying a victim, especially when there is a need to distinguish the victim from the assailant. In terms of family references, it is possible to employ different combinations of DNA from the victim’s family. For example, one or both parents of a victim may be employed to provide their DNA as reference sample in the identification of their son/daughter, who is the victim of a disaster. Another combination of a reference sample may involve the biological matter of the victim, together with their child or children. It is essential that the children be involved in this type of reference sample because it will show the mixture of STR patterns that are present in the child and the source can be determined, whether each STR pattern comes from either the father or the mother. A reference sample that only involves the biological mate will not be helpful to a forensic DNA analysis because there is no biological connection between the victim and the partner and thus the child or children should be included in a forensic analysis if the biological mate will participate in the forensic analysis. Siblings of the victim may also serve as reference samples for DNA analysis, as long as the sibling has at least one common parent with the victim. This common parent provides that biological or DNA connection between the sibling and the victim’s DNA, be it a paternal or a maternal biological connection in terms of STR patterns. Reference samples are often collected in the form of buccal swabs or blood and are processed for both nuclear and mitochondrial DNA.

In addition to DNA analysis, entomology may also be employed in crime scene investigation. The presence of insects in specific larval stages may generate information on the time of death of a victim. The information generated from such analysis may be combined with the data generated from DNA analysis to provide a bigger and more informative description of a crime or a disaster. The use of entomological data in forensic analysis may also provide information of the sequence of death of individuals in a crime scene. For example, if a mother and child were found dead in their home, the presence of insect larva at particular stages of development will provide information on whether the mother or the child died first. The sequence of death may be determined on the victim’s body by checking which larva is at a later stage of development, meaning that this victim died first and the other victim showing larva at a younger stage of development means that he died later. The weather, in relation to the presence of the larva, will also provide clues to the time of death of a victim. It is scientifically known that during winter, the insects take a longer time to migrate and produce larva, hence if a body is found during the winter, death must have ensued earlier because the larva presence in a body must that it must have taken some time for the insects to find this body and nest on it.

This type of crime scene investigation is usually associated with difficulties in isolating intact DNA due to the exposure of tissues to high temperatures of the fire. However, there have been frequent testing and optimization of DNA isolation protocols that it is now possible to increase the amount of DNA yield even if the tissue source has been burned in a fire or has been kept in preservatives such as formaldehyde for months, years, or decades (as in the case of mummified corpses). A better approach to DNA isolation involves the retention of the 0.5 mM EDTA solution with the pulverized bone in order to prolong chelation of calcium ions and other EDTA-inhibitors as well as the employment of collagenase for enzymatic dissociation of tissues (Schmerer et al. 1999). After such incubation, proteinase K will be introduced, as detailed in the original procedure.

The analytical power of crime scene investigation in combination with forensic analysis provides another powerful and reliable tool in the investigation of crimes and disasters (Alonso et al., 2005). However, it is important that precautionary measures be taken in order to prevent any false positive identification which is turn influence convictions of suspects as well as wrongful sentencing to either life imprisonment or death.

The act of crime scene investigation is designed to observe individuals, areas or objects that are of particular interest to an investigator in order to collect information and evidence that may be associated with a suspect and his related criminal activities (Walker, 2001). Physical surveillance is a method of examination of a particular area that is linked to a crime scene or a suspect. This may include inspecting the area where the crime took place, as well as the victim’s and suspect’s homes, vehicles, and paraphernalia. Examination will cover both the conditions of the places and items, as well as the position of the places and items in the particular areas.

Physical surveillance is important in a crime scene investigation because it provides a way for the investigator to reconstruct the scene and make inferences on what actually happened during the incident (Gardner, 2005). Any area that is associated with a crime is identified as soon as a crime has been established or reported. In addition, these particular areas are protected from any type of disruption by putting a crime scene tape along the perimeter of the area concerned. It has been reported that the most complicated part of an investigation is the establishment and protection of the boundaries of a crime scene because the signs related to a scene are often elusive to an investigator. Other investigators employ search dogs to facilitate the establishment and tracking of a crime scene.

Photography is commonly employed in the physical surveillance of a crime scene. This visual documentation of an area is very helpful to an investigator because it physically records the features of the area before any other activity is performed to the crime scene. Physical surveillance also involves marking all potential evidences to the crime. In addition to photographs, sketches of the crime scene are also important in physical surveillance of a specific area. Sketches are generally considered as essential information of crime scenes because these serve as detailed notes of the investigation, although the diagrammatic representation is of less quality than a simple photograph. Sketches provide measurements of the crime scene, including distances between two points of interest that are located within the area under investigation. An investigator often starts with a rough sketch and eventually moves on to a final sketch that is drawn to scale. These sketches are commonly employed as models during court hearings and trials because these provide the floor-plan of an area of interest, the elevation of the area and its details and other critical dimensions that may be helpful in the analysis of a crime scene.

Physical surveillance serves more purposes in a crime scene investigation than a technical surveillance because it provides the investigator with sufficient evidence that may be important in linking a specific suspect to a particular crime. Technical surveillance does not provide the specific details that physical surveillance provides because it does not provide any associative details that are critical to an investigation (Gottfredson and Hirschi, 1990). In addition, physical surveillance provides a view of the crime scene through an observer’s eyes and this usually provides a neutral view of the area, removing any biases and discrimination of certain items and areas. Physical surveillance also provides a better understanding of a crime incident through the note-taking that is performed on the area, including any traces of struggle or bullet holes. It also assists the investigator in reconstructing the sequence of events that are related to the crime, including the initial moments of what was said, done or executed by the victim and the suspect.

A forensic crime scene investigator is responsible for employing techniques in physical anthropology, human osteology and molecular analysis in criminal cases. A forensic crime scene investigator is trained in the identification of human bodies in different states or conditions such as decomposed, mutilated or burned. There are even cases wherein the human body is beyond recognition and it takes a forensic crime scene investigator to identify the person’s body in order to assist in further investigation a criminal case. The development of techniques in handling and analysis of human skeletal structures has influenced police investigators to rely on any information forensic anthropologists can offer (Prado et al., 1997). In combination with DNA analysis and the study of surrounding insects (entomology) and pollen (palynology), an efficient and effective method in investigating criminal cases can be conducted (Leclair et al., 2004). The inclusion of forensic data in criminal investigations has thus transformed the process of conviction and to a certain extent, has overturned particular verdicts upon review of old cases.


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