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Purine, Pyrimidine, and Prison: Evidence in the DNA

By Zubayer Mahbub

What comes to your mind when thinking of police or detectives solving a crime? For most, the mental image is quite standard across the board. Some see a detective, in a brown coat wearing a chic hat, equipped with a magnifying glass to get the best grasp of the available evidence. Others see a group of stern police officers, working together to interrogate witnesses, deeply scrutinizing the scene boxed off with lines of yellow tape reading “Crime Scene - Do Not Cross”, in front of them. The conjured image is strikingly similar to common scenes in thriller or mystery Hollywood movies.

But the reality in the 21st century is far from movie magic. The age of long, drawn-out investigations with a multitude of suspects, leads, and investigative processes has been coming to a rapid close. The one responsible for this transition away from traditional investigative work for a crime? DNA. Believe it or not, the truth lies in the 3 billion base pairs of Adenine, Cytosine, Guanine, and Thymine in the human body.

DNA, today, is used in countless ways during the solving of a crime. One of those ways is cross-referencing. Cross-referencing is where police compare DNA found at the scene of the crime to the DNA of a potential suspect. Crime scene DNA is found through stray hairs, skin cells, and more. Once police acquire this DNA, they hold onto it. When they have a suspect, police can take the DNA of the suspect and cross-reference it to the DNA at the scene of the crime, thus giving the method its name. If the DNA of the suspect is a match to DNA of the crime scene, law enforcement have more grounds to find a suspect responsible for a crime.

Another method is intrinsically tied to the first, and that’s the expansion of police databases. There are entire national databases of just DNA of criminals that police, around the country, use in their day to day. When police acquire the DNA at the scene of the crime, they log it into their database, searching for matches within the database. Even before police cross-reference crime scene DNA with the DNA of a suspect, they first cross-reference the crime scene DNA to DNA in their existing database to search for a match. If one is found, law enforcement can narrow their investigation down exponentially, making it far more likely they find who’s responsible.

The Federal DNA Database Unit (FDDU) and Federal CODIS DNA Database, for example, have over 11.4 million DNA profiles in their records. As of April 2017, the databases have assisted in a whopping 358,069 investigations. When more suspects are brought in, the databases continually grow, making future cross-references and assessments more likely to hit a match. In fact, of these investigations, many were cases where DNA was used to exonerate and prove suspects who had been assumed guilty to be innocent, saving them from serving a sentence for a crime they did not commit.

But even with all this new methodology and these grandiose results, DNA usage in crime investigation isn’t all sunshine and rainbows. There are still many who fundamentally oppose the usage of DNA in crime investigations for a multitude of reasons on the grounds of its ethics.

One concern is over the collection of DNA at a massive, national scale. Many believe that it is an unjust violation of one’s privacy for law enforcement to collect and hold on to one’s DNA, seemingly indefinitely. That’s because right now, DNA collection is relatively indiscriminate. If one is brought into a police station or holding facility, they are going to be fingerprinted or swabbed to collect their DNA, regardless of circumstance. This situation-blind collection of DNA leaves many questioning its validity. In fact, in 2020, 52% of Americans opposed DNA testing companies sharing information with law enforcement. How can DNA collection be morally just if it happens to all suspects, including the ones who are innocent? Is law enforcement justified in holding on to the DNA of innocent people too? The lack of answers to these questions has left a moral gray area that law enforcement is still attempting to navigate.

Another existing concern is over accuracy. The usage of DNA has left room for human error in the crime investigation process. Many are worried about the potential of lack of training, sloppy work and cross-contamination being involved in something as serious and consequential as criminal conviction. Even scarier, some are wary of the potential of trained criminals planting another person’s DNA at the scene of a crime to lead investigators astray, or even worse, towards a wrongful conviction. Pro-DNA usage citizens respond to these concerns by saying one can not be convicted solely on the basis of DNA; other things such as interrogations, witnesses, and even confessions are used and prioritized, thus making the likelihood of a wrongful conviction solely on the basis of DNA evidence unlikely.

Where do you stand on the pro-DNA to anti-DNA usage debate? Society is still going back and forth between advancing DNA usage and expanding its accessibility and usage and completely moving away from it altogether. While we may not ever get a clear answer to the debate, what we do know is that it is fascinating to think that infinitesimally small sequences of genetic information can hold so much bearing on the very fabric of our society and human life.

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