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Using DNA Profiling in Criminal Investigations

By: Srushti Nerkar

From: Princeton Junction, NJ, USA

The Golden State Killer

In 1967, the Golden State Killer crept quietly, without being seen, into a middle-class neighborhood, stalking each house for women who were alone. He made sure that their houses were next to some sort of exit such as a trail, creek or some open space. He climbed onto windows spying each house and frequently observing women and their daily routines to finally attack them at the right moment. When he was ready, he would climb the house, unlock the windows and hold a handgun to their foreheads and raped them. Joseph James DeAngelo was a truck mechanic during the day and was the Golden State Killer at night. He went on like this for the next 40 years, traveling throughout California without being caught by the police. At the time, fingerprints were used to determine who the killer was, but criminals could easily have worn gloves to keep their fingerprints out of sight. Would the Golden State Killer have been caught sooner if there was another way of finding who he really was?

The First Steps of DNA Analysis/Profiling

DNA analysis/profiling is when scientists extract DNA from a sample such as saliva, hair and etc, and use the genetic code to determine who was involved in a crime. The process of DNA profiling goes back 1984, where a genetics professor named Dr. Alec Jeffreys discovered that DNA could distinguish individuals since each DNA molecule was unique to each person. Before his experiment, he was testing out to see if he could trace genes within a family of species to see if there were repeated chromosomes in the DNA. First, he had to extract the DNA by using specific solutions to dissolve the other cell parts. Once the DNA was separated, he attached them to photographic films and used radioactive probes to determine which sequences in the DNA were repeated. He left the experiment over the weekend and came back to find that each individual DNA sample had a different barcode of its own. Two years after his discovery, he had helped solve a case using genetic fingerprinting to determine the culprit. This had completely changed tides for criminal investigations.

The Process of DNA Analysis

Now, technology has evolved and scientists are using more inventions for a more precise

analysis of DNA. As a result, scientists have to be careful and make sure that the experiment isn’t prone to errors. One of the first steps of DNA profiling, similar to Dr. Jefferys procedure is to extract the DNA sample from the cell. They use a specific solution to dissolve all the other cellular parts except the DNA. This process takes around 3 hours to complete. The next step is quantitation which is when scientists determine if the DNA sample is a human sample and by doing so, they measure the quality and quantity. This must be done so amplification can work efficiently. Amplification is done by a process called PCR (Polymerase Chain Reaction) which copies the DNA strand into millions of pieces. PCR, similar to DNA replication, involved heating and cooling DNA strands to multiply the number of strands. As a part of amplification, the DNA samples have to be put through a sex determiner marker to determine the sex of person using the DNA strands. Next, once the amplification process is complete, it results in the DNA molecules to be tightly packed, but they need to be separated from each other. Using Capillary Electrophoresis (CE), the negative charge on the DNA molecules is attracted to the positive end of the capillary, resulting in the DNA molecule moving toward the positive anode which separates the DNA from other molecules. Once the DNA molecules have been separated by size, it is now time to process the data in the DNA. The data is collected by a computer and is run by the software program to create the DNA profile. Finally, an instrument called ABI Prism® 3130 Genetic Analyzer analyzes each of the samples four at a time.

What happened to the Golden State Killer?

The Golden State Killer was finally caught in 2018, and the case was solved when the scientists used DNA analysis to determine if he was guilty. Investigators had obtained the victim’s DNA with a swab on the handle of his car door and saw that the DNA matched with the victim. He was then found guilty and was sentenced to prison for the rest of his life for his crimes. It was not until many years later that investigators found the suspect which shows that DNA profiling is key to solving many criminal cases.


About the Author: Srushti Nerkar

Srushti is a junior who is passionate about biology research in forensics. In her free time, she loves to watch Star Wars movies and find new DIY crafts to do.



  1. “Alec Jeffreys.” Wikipedia, Wikimedia Foundation, 20 July 2020,

  2. “Bureau of Criminal Apprehension.” Learn More about DPS, Divisions, Programs, Boards and Committees,

  3. “DNA Evidence: Basics of Analyzing.” National Institute of Justice,

  4. “Joseph James DeAngelo.” Wikipedia, Wikimedia Foundation, 4 Sept. 2020,

  5. McKie, Robin. “Eureka Moment That Led to the Discovery of DNA Fingerprinting.” The Guardian, Guardian News and Media, 23 May 2009,

  6. “How DNA Works.” HowStuffWorks,

  7. Burt, Chris. “DNA Profile.” Biometric, 2019,

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