DNA Profiling – The Robbery Case Study

DNA profiling involves the processes of identification and documentation of given regions of a DNA molecule to determine the origin of the DNA sample, to solve cases of uncertain parentage, to include or exonerate suspects of a certain crime, or to obtain relevant information in the diagnosis of certain genetic disorders. DNA profiling is also called DNA fingerprinting, DNA typing, or DNA testing. A scientist called Dr. Jeffreys discovered that DNA contains repeated sequences called Variable Number of Tandem Repeats (VNTRs). These variations are different and unique in different people, except for identical twins. He also discovered that one could develop a technique called Restriction Fragment Length Polymorphism (RFLP) to measure these variations. (Alamoudi et al., 2018). It is called a restriction fragment because it uses a restriction enzyme to cut the regions of DNA surrounding the VNTRs.

Significance of DNA Analysis in Solving Crimes

The unique genetic sequences in a person’s DNA make it possible to associate a person with a crime or exonerate a suspect from a certain crime. There are a variety of DNA tests applied in forensics to identify an individual, their sex, and personal traits. These tests are based on various molecular markers and include autosomal DNA, Y-chromosome DNA, X-chromosome DNA, and mitochondrial DNA. Autosomal DNA (atDNA) testing is the most commonly used testing. Autosomal DNA is packaged in the first 22 chromosomes, called autosomes. It is equally inherited; a child inherits one autosome from the father and the other from the mother. Before it is inherited, it is randomly shuffled in a process called recombination. Therefore, the child inherits random pieces of DNA from different ancestral branches (Genetic Science Learning Center, 2016).

DNA testing for forensic investigations utilizes biological material such as blood and bodily fluids collected from the crime scene. Thus, it is a valuable tool for solving criminal cases. For instance, DNA collected from the crime scene could be analyzed, and results could be compared with data from the DNA database to check for matches. A match, for instance, could indicate that the DNA from the crime scene and DNA from the database are identical, implying that the person from the database committed the crime. Similarly, if there are no matches, DNA evidence could be used to exclude the suspect from the crime.

Physical Evidence Retrieved from Crime Scenes

Crime scenes should be processed immediately after the case has been reported. Collection and preservation of physical evidence are important because it has a positive impact on juries in criminal cases: it proves that a crime has been committed; it can be used to place a suspect at the crime scene; it can be used to exclude an innocent person from a crime; it can be used to support statements from witnesses, and in some cases, suspects could confess if confronted with physical evidence. Physical evidence in the robbery case presented takes different forms, including fingerprints, blood, bodily fluids, and fired cartridges. Additionally, crime scene investigators (CSIs) are needed to take notes and photographs to describe the flow of events at the crime scene.

Since a physical confrontation occurred between the robbers and the male victim, it is essential to thoroughly search for fingerprints on the victim’s body or clothes as well as all the surfaces near the crime scene. Fingerprinting is also significant in learning about the suspect’s previous convictions, resulting in appropriate sentencing. There are three types of prints that provide relevant information concerning crime investigations. A latent fingerprint, for example, forms when the entire whorls of a finger containing a small amount of oil or grease are transferred to an object. Latent fingerprints include those that cannot be visible to the human eye; therefore, it is essential to examine the crime scene for these fingerprints carefully. Secondly, plastic fingerprints are formed on plastic materials when the finger presses against the material to leave a negative impression of friction ridges. On the other hand, dust and visible fingerprints are adulterated fingerprints. For example, a visible fingerprint is formed if a finger is placed on a layer of flour, ink, or blood and then placed on a clean surface.

Blood and other bodily fluids are valuable pieces of biological evidence placing or eliminating a person in a crime scene in scenarios where the blood is not only from the victims but also the perpetrator. DNA analysis of the blood could also be useful in determining the identity of the victims. This is especially important in such a case where the victims are foreigners from another country. Since the victims were shot, it is essential to search for firearm cartridges or shell casings. The location of shell casings could indicate the victim’s position, the angle of the weapon, and the range at which the firearm was discharged. Bullets, empty cases, and cartridges are beneficial in determining the type of weapon and the exact caliber used by the offender (Fisher & Fisher, 2012).

Impression marks resulting from the events at the crime scene should also be documented as they are powerful and valuable tools of evidence. Crimes like robbery result in the formation of a variety of impression marks; therefore, CSIs are needed to collect this evidence and take notes and photographs for admissible purposes. Impressions formed include foot impressions, car tire impressions, and tool marks. Tool marks are usually found on surfaces like doors or window frames. Additionally, evidence from glass fragments would be valuable physical evidence to collect. These fragments result from different circumstances. For example, a bullet that shatters glass can leave behind glass fragments on the surface and possibly on the perpetrator. Collecting these glass fragments would help investigators determine the direction of the bullet and its impact and match other broken pieces.

The Process of DNA Analysis

Criminalists follow several processes to examine biological samples and determine their source or origin. The first step is the collection of the biological samples. Biological samples range from body fluids to body tissues. For this case, biological samples containing DNA include blood and possibly sweat, saliva, and hair from the offenders. The second step is the extraction of DNA from its cells by using chemicals. The processes of DNA extraction include lysis, separation of DNA from the other cellular components, and finally, isolation of the DNA. Lysis is the disruption of the cell membrane, which is accomplished through the use of heat, detergents (sodium dodecyl sulfate), or dithiothreitol (DTT). Cellular proteins are then denatured using digestive enzymes like proteinase K. Finally, DNA is separated from the other cellular components through centrifugation (Elkins, 2012). The extracted DNA is then cut into small fragments using a restriction enzyme called endonuclease. The next step is gel electrophoresis. This technique is carried out to determine the quantity and quality of the extracted DNA. The DNA fragments are mixed with a sieving gel, and the process of electrophoresis sorts the particles based on their size and charge. By the end of this process, the yielded double-stranded DNA is separate from each other.

The next step is a technique called Southern blotting, which is used as a transfer method. In Southern blotting, the DNA is transported into a nylon membrane which is treated with radioactive DNA probes. These probes are single-stranded pieces of DNA complementary to the target DNA. Subsequently, the radioactive probe binds to the target DNA, and the results are viewed as images in an x-ray film. The excess probes are filtered out so that the resulting images can be analyzed visually or through computerized methods. Finally, the results are compared to other samples or DNA databases for matches. A match indicates that both samples came from the same source, while no match indicates no biological relationship between the two samples. The forensic specialist then writes a report explaining the findings of DNA testing.

Figure 1: The Process of DNA Profiling

Using the DNA Evidence to Convict the Suspects

All the analyzed evidence could be used to convict the suspects in the following ways. Firstly, DNA profiling results could be used to identify the two men who committed the crime and place them at the crime scene. The physical confrontation between the two men and the male victim implies that the two suspects left behind their DNA at the crime scene. The fact that two men have been previously arrested for assault and robbery means that their genetic information already exists in the DNA database. Therefore, when the DNA evidence collected from the crime scene was run through the database, it produced a positive match.

Similarly, fingerprint evidence could also be used to identify and place the suspects at the crime scene. Additionally, firearm evidence collected could be used to identify the exact firearm that was used to kill the victim. Follow-up investigations could be carried out to determine whether the suspects owned similar firearms. Finally, the identified suspects could make confessions when confronted by the crime investigators with all the collected evidence.

Conclusion

DNA profiling has become a valuable tool in forensic investigations. It utilizes the molecular biology of DNA and molecular markers to identify, include, or exclude persons from a crime. The process of DNA testing involves various procedures such as DNA extraction and techniques such as gel electrophoresis and Southern blotting. Samples that are relevant for DNA analysis include bodily fluids like blood and bodily tissues from cells like hair cells. CSIs should look out for physical evidence at the crime scene, ranging from firearms, blood, impression marks, and fingerprints. They should also take notes and photographs of the scene to describe the location of all items at the crime scene and also to describe events that show a crime took place.

References

Alamoudi, E., Mehmood, R., Albeshri, A., & Gojobori, T. (2018). DNA Profiling Methods and Tools: A Review. Lecture Notes of The Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 216-231. https://doi.org/10.1007/978-3-319-94180-6_22

Elkins, K. (2012). Forensic DNA Biology: A Laboratory Manual. Elsevier Science.

Fisher, B., & Fisher, D. (2012). Techniques of Crime Scene Investigation (8th ed.).

Genetic Science Learning Center. (2016). Introduction to Molecular Genealogy. Learn.genetics.utah.edu. Retrieved 16 January 2022, from http://learn.genetics.utah.edu/content/basics/molgen/

Lyman, M. (2011). Criminal investigation (6th ed.).

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Question

DNA Profiling – The Robbery Case Study

So far in this course, your study has concentrated on the origin, developmental stages, and many uses of DNA to solve crimes. You have studied how various body fluids, such as blood, saliva, and semen, are tested, and you have identified the importance of DNA and nuclear DNA in DNA profiling. Below are several case studies that were solved using the procedures and analyses studied in class, and the application of the information obtained was used to solve the criminal investigation.
Choose only 1 of the cases listed below and explain how the physical evidence recovered from the crime scene was tested and analyzed to solve the crime.
Case Study 1
A man and his wife were on vacation in Paris. On the way back to the hotel, they were approached by two men with weapons who demanded their jewelry. A physical interaction occurred in which the robbers violently wrestled the man to the ground and removed his watch and rings while his wife tried to run away. The man and his wife were shot and killed. The bodies of the two victims were pulled into an alley. Multiple scratches were on the body of the male victim, and blood was also found on the female victim because the robbers tore the necklace, rings, and earrings that she was wearing. The two men committing the crime both had previous records of assault and robbery. How were the men convicted of the crime?
Case Study 2
After 10 years of being free, a man was convicted of rape after DNA evidence was allowed to be used. The female he raped was not able to make an identification, so the attorney had to get permission to do a DNA profile on the suspect. The suspect had lived as a neighbor of the victim, only a few houses away. This man was considered a family friend; however, after the rape incident occurred, he abruptly moved to another state. How was he convicted or exonerated?

Assignment Guidelines
• Address the following in 4–5 pages:
What exactly is DNA profiling? Explain in detail.
 How it is used to solve crimes? Explain in detail.
Regarding your selected case study:
 What physical evidence would be retrieved from the crime scene?
 Identify each item of physical evidence and fully justify your decision to collect it as evidence.
 What type(s) of DNA tests are required to investigate the crime you have chosen? Explain in detail and fully support your argument.
 What is the testing process for the technique(s) used to test each piece of evidence? Be specific and explain in detail.
After analyzing the evidence, explain how the evidence exonerated or convicted the suspects.

DNA Profiling – The Robbery Case Study