Logan W.


Who Did It?

Although the flames disappeared early morning on March 8th, one critical piece of evidence was left behind – DNA. Originally, no one who was working in the factory saw the criminal who started the fire; however, through today’s modern DNA testing, no one needed to see the criminal in order for law enforcement for us to identify the arsonist.

Through a process called Polymerase Chain Reaction (PCR), the DNA found at the factory was amplified. The original DNA found in the factory was mixed with deoxyribosenucleotides, Taq polymerase and DNA primers. These DNA primers then hybridized to the specific sequence of DNA that was to be amplified, the primers then served as a starting point for the Taq polymerase. Next, this mixture is heated and cooled in order to break the hydrogen bonds in the DNA, creating single-stranded molecules. Cooling the DNA allows the primers to anneal to each end of the segment in order to be replicated. The Taq polymerase then begins creating the complementary strand of DNA, using the DNA primer as a starting point. The temperature is then raised in order to separate the DNA strands and lowered in order to allow the primers to attach. The Taq polymerase then creates another set of complementary strands. This process is repeated over and over again until enough DNA has been created to be used for further research in our case, further research is gel electrophoresis.




After the small sample of DNA was amplified, it could then be compared to other known arsonists’ DNA in a process known as gel electrophoresis. In the region of Northern Florida where the factory fire took place arson was becoming more and more popular, it is because of this law enforcement had multiple suspects in the investigation. It was shortly after the fire, law enforcement collected the DNA of the suspects in order to compare it to the sample found at the factory.

The process of gel electrophoresis can be explained as the following:

  1. A sample of DNA is harvested
  2. The end pieces are attached to the tray; meanwhile, the comb is added to the center of the tray.
  3. The gel is poured into the tray, cooled, and molded.
  4. Next the comb is removed and each DNA sample can be placed into each slot.
  5. Buffer solution is then added, covering the entirety of the mold along with the DNA.
  6. Finally, an electric current is applied.




The importance of the electric current is that it allows the DNA to be drawn out to show the different lengths. Each suspect has different DNA; thus, when their DNA is drawn out, each suspect  would have a different appearance of their DNA on the tray. In order to discover who started the fire, one just needs to look at the appearance of the DNA of the sample found at the factory and those of the suspects. The suspect’s DNA that matches the DNA found at the crime scene is the person who started the fire.

gel electrophoresis

The DNA test gel electrophoresis is not only used for catching criminals, it can also be used in paternity testing. In paternity cases, children receive 50% of their alleles from each parent; thus, the child should have a mixture of their parents alleles.  However, in this case, the purpose of gel electrophoresis was to determine the criminal who started the fire.

It was through DNA testing -PCR and gel electrophoresis that law enforcement was able to determine the criminal behind the fire, John Leonard Orr. Orr was in fact one of the original suspects whose DNA was compared to the original sample found at the crime scene. It was because of PCR the small sample was amplified, and it was because of gel electrophoresis the sample could be compared to the several suspect’s DNA samples; thus, leading to the eventual arrest of the arsonist.



  1. “Animation – Polymerase Chain Reaction.” Animation Quiz 6 – Polymerase Chain Reaction. N.p., n.d. Web. 30 Mar. 2016.
  2. “Gel Electrophoresis Overview.” Gel Electrophoresis Overview. N.p., n.d. Web. 30 Mar. 2016.
  3. “The Importance of DNA Testing for Society.” Why It Is DNA Testing Is Important. N.p., 23 May 2015. Web. 30 Mar. 2016.
  4. Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson Benjamin Cummings, 2009. Print.
  5. “Gel Electrophoresis.” Gel Electrophoresis. N.p., n.d. Web. 30 Mar. 2016.