Forensic science has evolved since it first emerged in antiquity, but few breakthroughs have been more impactful than DNA analysis.¹ The Boston Strangler, the Grim Sleeper, and BTK are just a handful of criminals who were found guilty with what many call the single most important development in forensic science history.^2,3

A powerful tool, forensic DNA analysis has gained increasing traction and credibility in the last few decades. It has the ability to accurately and objectively identify criminal offenders—and clear innocent persons who have been mistakenly accused or convicted.

But DNA analysis in forensic science isn’t as swift and straightforward as blockbuster films and hit TV shows may want us to believe. Whether you’re exploring the idea of pursuing a career in forensic science or simply want to know more about the subject, read on to learn how forensic DNA analysis has revolutionized criminal justice.

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The Basics of DNA Analysis

DNA analysis refers to examining deoxyribonucleic acid, or the genetic “blueprint” that exists in almost every cell in the human body.⁴

Given that no two people have the same DNA except identical twins, analyzing DNA in forensic science is widely considered a neutral, foolproof method of discovery in criminal investigations and civil cases.

According to the DOJ, DNA analyses are mainly used in one of two ways:

1. If a suspect has been identified in a criminal investigation, such as a murder, robbery, or sexual assault, DNA analysts can compare the accused person’s DNA to biological evidence left behind at the crime scene. This DNA testing may help investigators determine if they’re responsible.
2. If a suspect has not been identified, forensic scientists can run DNA samples against convicted criminal offenders in DNA databases. This system, known as the Combined DNA Index System (CODIS), was established in the 1980s to assist law enforcement agencies with investigations.

All of that said, some experts indicate that it’s easier to absolve a suspect than it is to convict an individual on a DNA match.⁵ Other factors in a crime are frequently considered, such as:

• Additional evidence 
• Weapons 
• Alibis
• Motive

Nonetheless, DNA analysis has a high level of accuracy, or around 99%.⁶

A Brief History of DNA Analysis 

The start of DNA analysis in forensic science is often credited to Alec Jeffreys, a British scientist who developed the first testing methods in 1985. By 1986, his DNA testing was used to solve a double homicide. A year later, DNA analysis led to the first conviction of a criminal defendant in the United States.

Since then, the National Institute of Justice predicts that DNA analyses have played a key role in the investigation and resolution of thousands of cases.⁷

DNA Collection and Preservation

Here’s how DNA analysis traditionally works in criminal investigations.

An investigator may gather physical objects that might have been touched or worn by individuals involved in a crime, such as bedding, dirty laundry, clothing, condoms, or toothbrushes.⁸

The first responding officer at a crime scene may then transport the evidence off the premises of the crime scene.⁹

Next, a serologist (or a scientist who studies bodily fluids) might be brought in to determine if the physical evidence contains a bodily fluid or other matter that can be analyzed for DNA.¹⁰ These include:

• Blood
• Semen 
• Hair
• Skin cells 
• Urine 
• Feces
• Vomit
• Sweat¹¹

If so, the evidence will be sent to a crime laboratory whose equipment and facilities meet the robust QAS (Quality of Assurance) requirements established by the FBI.

Preventing Contamination in DNA Samples 

Within all of this, you may be asking, is contamination during DNA extraction possible? Certainly.¹²

Contamination can occur at any stage, and location, in the process: At the crime scene itself, during transit, during the investigation of evidence, and in the crime laboratory. To this end, the National Institute of Justice urges law enforcement personnel to limit incidental activities at a crime scene. They’re also advised to keep physical evidence that may contain DNA in a cold environment and away from direct sunlight. Further, biological evidence should be air dried, packaged securely in paper, and labeled.

Contamination can also be caused by an individual not changing their protective gloves when handling evidence; this calls for stringent cleaning protocols. But here’s the good news: Contamination may be spotted and eliminated by comparing evidence against staff DNA profiles.

Still, avoiding contamination is crucial. A judge may throw out DNA evidence if the biological sample has been contaminated. Similarly, they may reject DNA evidence if the crime lab or the DNA analyst didn’t maintain quality control or use reliable methods.

Laboratory Processes in DNA Analysis

So, what are reliable methods? DNA analysis in forensic science typically goes through the following process:

• Extraction – “Extraction” describes the act of removing the DNA from a cell.
• Quantitation – During this stage, DNA analysts determine how much DNA they have to work with. Thanks to modern technology, this can be an extremely small amount—even dried saliva found on a cigarette butt left behind at the crime scene can help analysts draw up a DNA profile.
• Amplification – DNA analysts then use a method called polymerase chain reaction (PCR), which enables them to zero in on the DNA sample and make millions of copies of it. Why? To characterize it.
• Separation – Then, DNA analysts may separate the DNA fragments according to their size.
• Analysis and interpretation – Once the previous step is complete, DNA analysts can generate a profile and compare it against those contained in the database we mentioned earlier. This consists of DNA profiles on the local, state, and federal level, and contains profiles from convicted offenders, arrestees (in certain states), missing persons, biological relatives of missing persons, and unidentified human remains. It also includes DNA profiles on what’s known as “forensic unknowns,” or DNA profiles of unknown people from previous crime scene evidence.
• Quality assurance – The final phase is reviewing an analyst’s report to ensure technical accuracy.

Interpreting DNA Test Results

The results from DNA analysis fall into one of three categories:

• Inclusion – If the DNA profile of a suspect (or victim) aligns with the DNA profile pulled from evidence at a crime scene, the person in question may be included as the potential source of such evidence.
• Exclusion – When the DNA sample doesn’t match with the DNA profile produced at a crime scene, that individual is “excluded.” This, however, doesn’t necessarily suggest innocence.
• Inconclusive – A DNA analysis is thought of as “inconclusive” if the results can neither include or exclude a person as a potential source of the biological evidence discovered at a crime scene. This may be due to a number of reasons, such as contamination, or issues with the quality and quantity of the DNA sample.

All told, DNA analysis may have to be repeated. As mentioned, the entirety of a crime scene and its context is also taken into consideration. But should DNA analysis succeed, it can—again—lead to justice.

Who Performs DNA Analysis?

DNA analysis requires an exceptionally high level of accuracy and reliability, as well as objectivity, fair, appropriate reporting skills, and a facility with a crime lab’s testing equipment.

But how does one get there?

DNA analysts usually must possess a minimum of a bachelor’s degree in a relevant subject, such as:¹³

• Chemistry
• Biology
• Forensic science
• Physics
• Medicine
• Biomedical science

Some DNA analysts may also complete an apprenticeship prior to heading into a crime laboratory. For those aspiring to this field, understanding how to become a forensic scientist is a critical first step.

Further, DNA analysts who work in a crime lab must remain current on the latest practices and technologies in DNA and forensic science. This can be accomplished through continuing education (CE) programs that fulfill the FBI’s Quality of Assurance Standards (QAS). Continuing education programs are crucial for maintaining these forensic scientist skills.

Applications of DNA Analysis in Forensic Science

As you can see, DNA analysis has become a cornerstone of the criminal justice system.

It’s also become increasingly advanced with the introduction of forensic genetic genealogy (FGG), an investigative technique that merges DNA profiling with genealogy research to produce investigative leads in unsolved violent crimes.¹⁴

Since 2018, the combination of these tools have, by some estimates, helped solve 500 murder and rape cases—most notably, the identification, apprehension, and prosecution of the “Golden State Killer,” Joseph James DeAngelo.¹⁵

More recently, the blend of DNA analysis and FGG helped solve the murder of Teree Becker nearly 50 years after it occurred; this was accomplished through the use of DNA technology and CODIS.¹⁶ And while the culprit had died by suicide years earlier, it provided a sense of closure for Becker’s family.

Ultimately, this is one of the greatest gifts DNA analysis can offer: Resolution, even after decades of waiting.

The Future of DNA Analysis in Forensic Science

DNA analysis plays an integral role in forensic science and the criminal justice system. It’s been hugely instrumental in identifying criminal offenders, exonerating those who have been wrongly convicted, and finding justice for crime victims and their families.

If the idea of becoming a DNA analyst intrigues you, Alliant International University may be the perfect place for you to advance your education. The MS in Forensic Science, Investigation, & Technology offers students with the training and knowledge they need to make strides in their career. The program also provides a holistic view on the field of forensics, with courses that focus on ethics, cultural competencies, the law, and documentation.

Fulfill your academic journey at Alliant International University.

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Sources:

1. Historical references and doctrinal precedents of forensic ... Ahttps://rais.education/wp-content/uploads/2023/07/0290.pdf. 
2. Sharp, Nathan. “Top 10 Cold Cases Solved with DNA: Articles on Watchmojo.Com.” WatchMojo, July 17, 2024. https://www.watchmojo.com/articles/top-10-cold-cases-solved-with-dna. Accessed July 17, 2024. 
3. “Advancing Justice through DNA Technology: Using DNA to Solve Crimes.” Office of the Attorney General, March 7, 2017. https://www.justice.gov/archives/ag/advancing-justice-through-dna-techn…. Accessed July 17, 2024. 
4. “When DNA Samples Are Complicated: Calculating Variation in Mixed Samples Interpretation.” National Institute of Justice. https://nij.ojp.gov/topics/articles/when-dna-samples-are-complicated-ca…. Accessed July 18, 2024. 
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8.  “DNA Evidence.” DNA Evidence: How It’s Done. https://www.forensicsciencesimplified.org/dna/how.html. Accessed July 18, 2024.
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10. “Forensic Biology & DNA.” NCDOJ, September 11, 2020. https://ncdoj.gov/crime-lab/forensic-biology-and-dna/. 
    Accessed July 17, 2024. 
11. Understanding DNA evidence. https://www.ojp.gov/pdffiles1/nij/bc000657.pdf. Accessed July 17, 2024. 
12. “The Risk of Contamination in Forensic DNA Profiling.” Forensic Access. https://www.forensic-access.co.uk/news/insight/the-risk-of-contaminatio…. Accessed July 18, 2024. 
13. How to become a DNA analyst (plus skills and faqs). https://uk.indeed.com/career-advice/finding-a-job/how-to-become-dna-ana…. Accessed July 17, 2024. 
14. Forensic genetic genealogical DNA analysis and searching. https://www.justice.gov/olp/page/file/1204386/dl. Accessed July 17, 2024. 
15. Mullin, Emily. “A Nonprofit Wants Your DNA Data to Solve Crimes.” Wired, March 23, 2023. https://www.wired.com/story/genetic-genealogy-nonprofit-dna-database/. Accessed July 17, 2024. 
16. “50-Year-Old Colorado Cold Case Solved after DNA Technology Identifies Woman’s Killer.” NBCNews.com, February 1, 2024. https://www.nbcnews.com/news/us-news/50-year-old-colorado-cold-case-sol…. Accessed July 17, 2024.