To properly being able to discuss this essay in-depth, it's necessary to understand first what the term serial killer means. The proper definition of a serial killer is the illicit murder of at least two victims or more committed by the same person, but in different times and places. This term, it's often been confused and it's hard to distinguish with the term mass murder, which is defined as murders that took place at the same time and place committed by the same person. Throughout the years, there has been some discussion about the adequate definition of a serial killer, as there are a few aspects that need to be taken into account when considering a perpetrator, a serial killer. (Federal Bureau of Investigation, 2010) (Serial murder | Definition, Characteristics, Types, & Facts | Britannica, 2020).
The discipline of forensic science is crucial in a variety of aspects in the legal system. In the court, a forensic scientist acts as witness expertise. They provide reliable and impartial knowledge about the pieces of evidence that were collected from the crime scene, which were later investigated in a laboratory using different forensic techniques. It can introduce key arguments that will define whether the alleged accused was in any way present the moment the felony took place or on the contrary, it can prove that they are being accused wrongfully. The field is also used when investigating a case, it can offer a breakthrough in the case and often leads to the capture of the perpetrator. (Jackson and Jackson, 2008).
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To demonstrate how the advancement of techniques in forensic science was used for the prosecution and identification of different perpetrators, two notorious serial killers will be considered.
Gary Ridgway
The case for the first serial killer was solved entirely as the result of the development of new DNA techniques almost 20 years after his first victim. Gary Ridgway committed his first five crimes between July and August of 1982, the bodies of his victims were found on the shores of the Green River on the King's County, WA. Hence his serial killer name, the Green River killer. (Levi-Minzi and Shields, 2007) (Palenik, 2009). By 1984, the police department was able to link at least 20 deaths to the Green River killer. (Levi-Minzi and Shields, 2007). His victims were mostly women prostitutes that he would rape and later killing them. (Svoboda, New York Times, 2009). Gary Ridgway was captured on the 30th of November of 2001 while working as a spray painter. This was not his first encounter with the police department, as, in 1982, he was arrested on charges of soliciting prostitution. However, in 1983, he became a person of interest in the Green River case, so he was brought to the police station for interrogation where he completed and passed a polygraph examination. After this test, he was released and was no longer in the attention of the police. Nonetheless, in April of 1987, the authorities were interested in him again and took hair and saliva samples, along with a search in his property. (Douglas and Olshaker, 2017) (Levi-Minzi and Shields, 2007). He was charged for the first-degree murder of forty-nine victims in 2003 after he pleaded guilty to avoid the death penalty. (Douglas and Olshaker, 2017). He later claimed that his total killing count could be of up to 90 victims. (Lackey, 2019)
During the investigation of the first crime scene, DNA was found. (Maleng, 2004). But, as it was at the early stages before any proper DNA analysis was created, the samples were in no way useful for the identification of the serial killer. However, in 2001, new DNA techniques were discovered and finally, the samples took from different crime scenes and the samples that Gary Ridgway provided were a perfect match, therefore confirming his identity as the Green River killer. The DNA methods used for his identification were the short tandem repeat (STR) and the polymerase chain reaction (PCR). STR is a short part of the DNA that contains different pairs of bases, each individual has a different number of base pairs and different lengths of them. The PCR technique is linked to STR. The method separates STRs from the DNA helix and then forms several copies of it. To be able to confirm that Gary Ridgway was the serial killer, the test needed to have a positive confirmation of over 13 of the STRs to match between the samples collected from him and the samples from the crime scene. (Balangue, 2018).
Once he was captured, investigators were trying to provide more forensic evidence for the prosecution of Gary Ridgway. So, in July of 2002, a forensic scientist was contacted by the police to examine further microscopic paint particles that were extracted from different crime scenes and some clothing of the victims. He needed to provide an answer whether these specific particles match any paint particle obtained from Gary's locker, home or car. Unfortunately, the match was negative and there wasn't any linked between them. However, after re-exanimating different victim's clothes, it was noted that there were quite a large number of sphere spray paint particles, which were a match to the spray paint that he used at work. This helped in connecting him with 6 more victims. (Palenik, 2009)
Albert DeSalvo
The case for the second serial killer is quite different from the previous one. The accused, Albert DeSalvo was charged on rape charges that were not related to his activities as a serial killer in Boston. Later in prison, he finally confessed to the killing of 13 victims between 1962 and 1964. His method to execute his murders would be to rape his victims and afterwards, strangle them to death, hence his label as the Boston Strangler. He was then assassinated in 1973 while in prison. When he confessed his crimes, there was some doubt about his identity as the Boston Strangler, so in 2013, the National Institute of Justice of the USA, funded the reopening of the case to try to obtain a final answer. (National Institute of Justice, 2020) (National Institute of Justice, 2014).
When these crimes took place, the analysis for DNA was almost inexistent, so it was difficult to match the culprit with any DNA evidence that was collected from his victims or in the crime scene. One of his last victims, who was Mary Sullivan, was murdered in January 1964 and when the team of forensic scientists investigated the crime scene, they were able to collect seminal fluid from Sullivan's body and on a blanket at the crime scene. Almost 48 years later, these samples would be the key to finally resolve the true identity of the Boston Strangles. (National Institute of Justice, 2014)
In 2012, the Boston Police department reopen the case through a cold case program. They asked the nephew of Albert DeSalvo's to provide a DNA test to match it with the seminal fluid found on Mary Sullivan's body. The forensics team used the technique of Y-chromosome short tandem repeats (Y-STRs), where it shows that every single male member in the family has the same Y-STR DNA profile. So, when this method was used to match the evidence from the crime scene and the DNA sample from the nephew, it ended up being a positive result. This means, that any male member of the family DeSalvo was associated with the murder, this test also eliminates 99.9 per cent of the male population. They then decided to go a step further and be more precise with their technique, as it doesn't provide an individual result and exhumated Albert DeSalvo body to obtain direct DNA from him this time. They extracted DNA from his femur and three remaining teeth. With these samples, they were able to obtain a perfect match that confirmed that Albert DeSalvo did rape and killed Mary Sullivan. (National Institute of Justice, 2014)
Discussion
In this section of the essay, the advantages and disadvantages of the two techniques used for the investigation and capture of the Green River killer and the Boston Strangler will be review.
For the examination of a DNA evidence sample, the PCR technique is used, which consist of the DNA extraction, quantification and the STR amplification. A key disadvantage during this whole process is the possibility of the loss of DNA. The DNA polymerase used in the technique is likely to be predisposed to errors and as a result, it can cause some mutations in the section generated. The section generated by PCR can be altered by nonspecific binding of the primers to other similar sequences on the template DNA. (Garibyan and Avashia, 2013)
One of the main advantages of PCR is that it allows rapid amplification of the required section of DNA and with enough sample, it can create a large number of copies, which can be used for the detection and identification of gene sequence by using visual techniques based on size and charge. A new improved version of the PCR can maximise the quantities of DNA to be targeted, which at the end reduces the opportunities for error and contamination during the whole process. (Garibyan and Avashia, 2013) (Cavanaugh and Bathrick, 2018). Another advantage is that when there is a match of over 13 STRs between samples, it means that there is a possibility that 1 in a trillion chance, someone else has the same amount of STRs as the individual in question. (Balangue, 2018).
The main advantage of the Y-STR technique and why is so useful in the forensics field is because it's able to recognise the Y-chromosome gene fragment, and therefore concluding the biological sex of the sample. In sexual assault cases, even where there is a high mixture of female and male DNA, still the technique would only recognise the male DNA. Any sample analysed with this procedure will acknowledge all the male members of the sample's family, as they have the same Y-STR DNA profile. In a case, this narrows the investigation and provides a step forward in the identification of the perpetrator. (Kayser, 2017) (Prinz, 2020)
On the contrary, the main disadvantage that the technique presents is that it doesn't differentiate male relatives, it only gives a general idea about the family. (Prinz, 2020). This means that it's harder to obtain a solid identification of the offender. Also, to be able to do this technique the DNA of any male member of the suspect's family is necessary, but the acquisition of the require sample can be hard if there are no leads at all in the case and the family of the suspect is completely unknown.
Conclusion
From all the information gathered throughout the essay, the continuous development in new DNA techniques and the willingness of scientists to take the field of forensic science a step further was extremely vital to provide the real identity of the Green Serial killer and the Boston Strangler.
In the Green River case, it can be observed the reality of what happens when the techniques available at that time are precarious, and because the PCR technique was still not developed, Gary Ridgway was able to continue committing his crimes, taking the lives of around 90 victims. Even though the forensic scientists investigating the first crime scene knew there were not enough DNA techniques, they still recover DNA samples, believing that in the future a technique would be developed and as a result of this, 20 years later, he was found guilty and finally incarcerated, thus achieving justice for his victims.
For the case of the Boston Strangler, Albert DeSalvo was never convicted for his crimes, nonetheless, he did confess to the murders and then he was questioned about it. So, with the apparition of the Y-STR technique and the predisposition of his family to cooperate with the police once the case was reopened, the mystery was finally resolved and it concluded that he was the Boston Strangler.
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