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.
Forensic crime scene investigation currently employs the study of human remains and this also involves extraction of deoxyribonucleic acid 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 geometrically 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. If the results show a different DNA profile, then the suspect can be indicted from the criminal investigation.
However, if the DNA profile from the STR analysis is not different, the suspect can not be 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, which determines that chances that an individual selected at random would have a similar DNA profile with those STR sequences that 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.