DNA fingerprinting has become one of the most powerful tools in modern criminal investigations. Thanks to scientific and technological advancements, law enforcement agencies rely on DNA to solve crimes, confirm identities, and even exonerate innocent parties. But just how reliable is this type of evidence? Can someone be convicted based on DNA alone?
What Is DNA Fingerprinting?
DNA fingerprinting is also known as DNA profiling. It’s a method used to identify a person by examining their unique genetic makeup. The term has nothing to do with actual fingerprints. Instead, it refers to analyzing specific regions in someone’s DNA. These regions vary widely between individual people, which makes it possible to identify potential perpetrators – or rule them out.
Every human has a unique DNA sequence, except for identical twins. DNA fingerprinting looks at short tandem repeats (STRs). These are sections of DNA that can serve as identifiers since they are highly variable. The technique was introduced in the 1980s and is now a cornerstone in forensic science.
In New Jersey, DNA fingerprinting is managed in part by the New Jersey State Police Office of Forensic Sciences. Their DNA laboratory, accredited by the ANSI National Accreditation Board, processes thousands of samples each year for use in criminal cases.
How Does DNA Fingerprinting Work?
The DNA analysis begins with collecting a biological sample, such as blood, saliva, skin cells, or hair follicles. These samples are often found at a crime scene, on a weapon, or on a victim or suspect. Once collected, law enforcement sends the samples to a laboratory for analysis.
The process typically involves:
- Extraction – First, the technicians isolate the DNA from the cells in the sample.
- Amplification – The lab uses a process called polymerase chain reaction (PCR) to make millions of copies of specific DNA regions.
- Separation and detection – Next, the DNA copies are separated and visualized using electrophoresis to create a profile.
- Comparison – The resulting DNA profile is compared to known samples or entered into CODIS, the Combined DNA Index System. This is a national database used by law enforcement.
The entire process can take anywhere from several days to weeks. The timing usually depends on the lab’s backlog, the sample complexity, and how urgent the case may be.
How Is DNA Fingerprinting Used in Criminal Investigations?
DNA fingerprinting can be used in several ways:
- Identifying suspects – If a DNA profile from a crime scene matches a suspect’s profile, prosecutors may use it to place that person at the scene.
- Linking crimes – DNA from one case may match DNA collected in a separate investigation, helping law enforcement connect the dots. For example, the Golden State Killer was linked to multiple crimes (and eventually apprehended) using DNA evidence, decades after the offenses happened.
- Exonerating innocent suspects – DNA can prove that someone did not commit a crime when the biological material excludes them as the source.
- Confirming victim identities – In homicides or mass casualty events, DNA also helps identify remains.
Under New Jersey’s DNA Database and Databank Act of 1994, anyone convicted of certain offenses must submit a DNA sample. This information can be used in future investigations, even years after the original conviction. However, the law also sets rules and procedures that must be followed when collecting, analyzing, using, and storing DNA.
Is DNA Enough to Convict Someone of a Crime?
While DNA is often viewed as a smoking gun, it’s not always enough to convict someone by itself. Its strength depends on several factors:
- How and where the DNA was found – A sample on a murder weapon carries more weight than a partial sample found on a doorknob nearby.
- The DNA’s quality and quantity – Degraded or mixed samples are harder to interpret.
- Chain of custody and lab integrity – If a sample is mishandled or contaminated, its credibility may be questionable.
DNA fingerprinting and forensics aren’t infallible, and convictions based on DNA evidence have been overturned before. Importantly, DNA alone doesn’t explain how or when it got there. For example, your DNA could be found in a friend’s car because you rode in it, not because you committed a crime there.
Courts in New Jersey and elsewhere recognize these limitations. Prosecutors try to corroborate scientific evidence with other proof to secure a conviction. This might include witness testimony, surveillance footage, or confessions.
How Criminal Defense Attorneys Can Challenge DNA Evidence
An experienced criminal defense attorney can take several approaches to challenge DNA evidence:
- Questioning the source – Just because DNA was found doesn’t necessarily mean the defendant committed the crime. An attorney can argue there’s an innocent explanation for its presence.
- Challenging the collection or testing process – DNA results could be inadmissible if law enforcement or scientists failed to follow proper procedures. Contaminated or improperly collected samples could give inconclusive or false results.
- Highlighting lab errors – Mistakes happen, even in accredited labs. Cross-contamination, mislabeling, and poor documentation can all lead to inaccurate results.
- Disputing the interpretation – A mixed DNA sample (containing material from more than one person) can be difficult to analyze.
Depending on the evidence, the defense can call forensic experts to conduct an independent review or retest of the DNA. Forensic scientists and prosecutors are not immune to junk science or flawed methodologies. Defense attorneys may highlight inconsistencies or poor handling to expose evidentiary weaknesses.
Get in Touch with Our Criminal Defense Attorneys in New Jersey Today
Although DNA evidence can be compelling, it’s not perfect. DNA can be misused, misinterpreted, or overstated in court. If you’re facing criminal charges, you need an experienced criminal defense attorney who understands science and the legal system.
The Law Offices of Jonathan F. Marshall has defended countless clients across the state. With over 200 years of combined legal experience, our skilled criminal defense lawyers know how to scrutinize DNA evidence from every angle and show when the evidence is flawed. When you work with us, we’ll review the evidence, conduct our own investigations, consult independent experts, and fight for a fair result. Whether your case can be resolved through dismissal, acquittal, a plea deal, or another option, we’ll fight to protect your rights.
Contact us for a free consultation and start building your defense today.
