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Inside of each cells in the human body, there are components of genetic material called chromosomes. Along these chromosomes, there are millions of genes, which are the fundamental unit of heredity and are composed of DNA. DNA is the substance by which genetic instructions are passed from one generation to the next.
The development of DNA a in criminal
In 1869 Friedrick Miescher discovered a section of DNA and noted that is was linked to our genetic make-up, but unfortunately, its significance at that time was not fully understood. Throughout the twentieth century, more studies were conducted on the structure and use of DNA and in 1953, James Watson and Francis Crick suggested a model for DNA that is generally accepted as being the discovery of its structure.
Prior to mid-1980s, blood found at a crime scene, would only be classified into type A, B, AB and O by the forensic scientists. But in 1985, Professor Alec Jeffreys from the University of Leicester suggested that DNA 'fingerprints' were specific to an individual and could therefore be used as a mean of identification, including testing for 'parent-hood'. Moreover, Jeffreys also created a chart for comparison, which is known as proofing.
Jeffreys' proofing techniques was first put to the test in 1986 in a case in which two schoolgirls had been rape and then murdered. The main suspect for the two rapes was profiled using Jeffreys' technique and cleared of leaving the DNA evidence, in the form of semen on the victims' clothes. Even though samples from 4582 men were taken, none of them matches the DNA founded from the scenes. Later on, the police were informed that Colin Pitchfork, had persuaded a colleague to present himself as Colin so that he would not have to give a blood sample. Colin Pitchfork was immediate arrested and when a blood sample was taken, the DNA proofing of Pitchfork matched those from the crime scene. Even though this process was successful, in good condition and relied upon the sample being rich in DNA, it was also unsuitable for the inclusion of results on a computer database. Therefore another process was developed, which took the same of SLP, single locus probe. Initially developed by ICI then taken on by mainstream forensic science provider, this process really advanced the DNA technology. it looked at four preselected sites on the DNA and was far more sensitive, being able to differentiate between mixed stains. Than in 1990s, a technique known as PCR, polymerase chain reaction was developed which enabled scientists to amplify material from small amount of DNA.
In 1995, the forensic science service established the first national DNA database, which contains the DNA profiles of people suspected, charged or convicted of recordable criminal offences and also the DNA samples recovered by the CSIs from the crime scenes.
Since then, DNA, which stands for deoxyribonucleic acid, has become the most powerful single tool in the complex fight against crime and no other forensic tool enjoys the level of confidence that DNA inspired for justice officials and juries. It is also, a valuable evidence in a crime investigation and can be collected from virtually anywhere and found in many forms at a crime scene, such as semen, blood, hair, ear wax and even saliva on face-marks or cigarette ends. All it takes is a few cells in order to obtain enough DNA information.
The contribution of DNA in the Grim Sleeper case
In mid 1980s, a lot of detectives fail to track the killer known as the Grim Sleeper Killer, responsible for at least the death of ten women, but a new technique and a discorded piece of pizza, Franklin DNA matches the DNA from the crime scene. In fact it was not a witness of some sort of information that led to the identification of this serial killer, who had escaped the police more than two decades, but the DNA from the suspect's own case. A new technique which is known as the familial DNA led the police to "57 year old" Lonnie David Franklin Junior, who was previously charged with ten counts of murder and one count of attempted murder.
The contribution of DNA in other cases
The use of DNA technology was not only useful in the Grim Sleeper case, but also helped in the review of a twenty-three year old murder case, where a "38-year-old" woman was sexually assaulted and violently murdered. In September 2000, Ian Lowther was found guilty of the murder of Mary Gregson, and was sentenced to a life imprisonment. During the investigation into her death, a sample of semen was recovered from the victim's clothes. This sample was then grouped according to the blood type, since at that time the DNA process was unavailable. Although a large number of individuals were interviewed, no one was convicted of the crime. Developments in DNA technology over the following 23 years supplied a tool that allowed a re-examination of the evidence from the case. Using low copy number of DNA, a profile was obtained from the semen stain on Mary Gregson's clothing. A mass screen, taking DNA buccal swabs from individuals questioned during the initial investigation, led to a successful match with the DNA proofing from the semen stain. This was a real success for the use of modern technology in the examination of unsolved crime.
Another case in which investigators used the DNA technology is the case of a serial killer in German. For many years, police tried to trace him, but only in 2007 the case exploded. Thanks to the Dna evidence which was found at the scene, police realized that the suspects is the same person who has been present at numerous murders and burglaries.
Pros and cons of DNA in a criminal investigation
In contemporary society, DNA is described as the "gold standard for identification". This is due that DNA can offer a lot of benefits. Apart from being inclusiveness and effectiveness, it is also intrusiveness.
This technology instead of being used "reactively, it is used inceptively." Therefore, it shapes an inquiry by identifying potential suspects from the beginning and not simply supporting their incrimination or liberation after they have been nominated for attention by other forms of investigative practice.
Moreover, there has been a lot of laboratory improvement which enable the "reliable extraction of genetic material from a wider range of samples in varying conditions". This also meant that now-a-days it is easier for forensic laboratories to generate DNA profiles. This also helps to ease the investigation and the prosecution of a larger number of crime types.
Apart from these, DNA offer more benefits. Such benefits include, the ability to easy eliminate innocent suspect from investigation and the ability to make immediate and strong suspected offender identifications through automatic profile comparisons in national criminal justice database. Moreover, DNA tends to generate very reliable and persuasive evidence to be used in court. Also, DNA technology not only helped to reduce the cost in many investigations, but helped in the increase of public confidence in police and it the national judicial process.
Like any other tool, DNA even though it has brought a dramatic change in the criminal investigation and identification of human beings, it has also some limitations and challenges.
The spread of forensic DNA profiling and data basing has provoked a lot of concerns about problems that may emerge from the "storage of tissue samples, especially those taken from individuals without their consent and the proliferating uses of genetic information by the police." Due to this, in jurisdictions, where forensic DNA database have been introduced, a series of critical comments have emerged. Some of these comments focused on the "privacy rights caused by the storage and use of tissue samples and the potential for the future misuse of such samples."
Moreover, even though DNA testing does don't lie, it can sometimes be misleading as happened in the case of a mother who almost lost her children and was under suspicion. The reason behind this was that her DNA did not match with that of her children. After a lot of research, police noticed that the women had a condition names 'chimera' and that her DNA in her blood did not match the DNA in other parts of her body.
Furthermore, there can be the possibility of tampering, or in other words, corrupt police officers or crime lab personnel can tamper with DNA results. Also, there might be some sort of accidents, by which DNA results become tampered.
Precautions that need to be taken when working with DNA
Information gained from investigation of data
DNA is not only helpful in the identification of people, but from it police can gain some ideas what really happened on the scene and in what sequence the events occurred. Through data investigation and the examination of the direction the blood was traveling when it hit a surface, police are able to identify the direction from which any force was applied. Also, investigators can identify the angle at which it hit the surface and even the amount of force involved, since the harder the victim was hit, the smaller the splash on the surface. From data investigation, it is also possible to detect the minimum number of blows struck.
Blood, which has a greater than 80% chance of revealing the DNA profile of the offender, is not the only source from which police and investigators can obtain DNA at a criminal scene but semen and saliva are also a strong sources of DNA.
Semen, which is present at a scene of a sexual assault, can confirm or disprove the victim's or suspect's story as to the sequence of events. Also semen stain has a high possibility of 70% in revealing DNA profile.
On the other hand, saliva which was a fundamental source to solve the Grim Sleeper case, can be found on any item has been bitten, chewed or spat on it. Moreover, if collected well it has a 40% possibility of revealing a DNA profile.
3 samples that can be taken from a suspect to obtain DNA profile
The most common and known method is the taking of blood from a professional doctor. Normally all is needed is a 5 "ml" of blood. After the blood is taken, it is placed in a container coated with a preservative called EDTA. Then this sample is frozen prior to transport to the forensic service provider.
Another common form of taking sample of DNA is the mouth swab sample kit. Two swabs are worn down the inside of the cheeks, buccal cells that are present in the mouth are collected and these are then stored frozen. This method has proven to be very successful and it has been extended to offer an elimination database of police employees if they accidentally leave their DNA at a crime scene.
Another method, but which is less common is the plucked head hair with roots. Since the roots will also reveal a DNA profile, it is easy to obtain DNA from a plucked head hair.