Explaining DNA Evidence to a Jury: Best Practices for Attorneys

DNA evidence can be a decisive element in criminal cases by providing powerful scientific proof of identity. However, explaining forensic DNA results to a jury—especially those without a science background—can be challenging. Misinterpretation or confusion can weaken even the strongest DNA evidence. Attorneys must bridge the gap between complex DNA analysis and clear, compelling narratives.

DNA evidence can be made more accessible and persuasive by breaking down key concepts into simple explanations, using visual storytelling, and leveraging expert testimony.

The Challenge: Making DNA Evidence Understandable

Many jurors are familiar with DNA testing from TV and podcast crime dramas, but real-world forensic DNA analysis is far more nuanced. A fundamental challenge in court is overcoming misconceptions and ensuring that jurors grasp:

How DNA is collected, tested, and analyzed.
What DNA evidence can and cannot prove.
The laboratory work was performed correctly.
The significance of statistical probabilities in DNA matches.
The scientific reliability of forensic DNA testing methods.

Jurors do not need to be DNA experts, but the evidence must be presented in a way that allows them to understand its significance and make an informed decision.

Best Practices for Explaining DNA Evidence

1. Use Visual Storytelling

One approach that may help explain forensic science involves using comics and visual storytelling to explain complex concepts in court (see comics here.) This approach helps jurors retain information by breaking down complicated processes into simple, sequential imagery. Attorneys should consider:

Diagrams of DNA Structure & Testing Process: Show how DNA is extracted, amplified, and analyzed.
Probability Charts: Use simple graphics to illustrate match probabilities, making statistical evidence more digestible.
Case-Specific Infographics: Highlight key findings from the case using easy-to-follow visuals.

A well-designed visual can clarify months of forensic analysis in seconds and reinforce key points for the jury.

2. Break Down DNA Results in Layman’s Terms

Avoid technical jargon and focus on analogies that make complex concepts relatable. Examples include:

“DNA is like a fingerprint but at the molecular level.”
“Think of DNA like a barcode—each person’s is unique, and forensic testing is how we scan and match it.”
“Matching DNA is like finding a puzzle piece that fits exactly, but we also calculate how often that piece could randomly appear.”

Attorneys should rehearse explanations with expert witnesses before trial to ensure clarity and impact.

3. Probabilities and Statistics

One of the biggest hurdles in DNA cases is explaining probability and match statistics. Jurors may hear that a suspect’s DNA profile matches “1 in 10 billion” individuals and mistakenly believe this means absolute certainty. It’s essential to explain that there are different statistics that can be involved:

Likelihood Ratios: A statistical measure comparing how much more likely DNA came from the suspect than a random person. Higher ratios strengthen the evidence supporting that the suspect’s DNA is present.
Random Match Probability (RMP): This number represents how often a given DNA profile might randomly match someone unrelated to the individual in the population. Lower numbers (as in 1 in a large number such as a quintillion or septillion) indicate stronger evidence supporting that the individual was the source of the DNA.
Exclusions vs. Inclusions: Make clear that while DNA matches provide strong support for identity, exclusions definitively rule someone out.

Likelihood ratios are used more frequently in court than RMP by experts because they typically provide a more accurate assessment, particularly in complex cases involving degraded or mixed DNA samples. Likelihood ratios are especially helpful with mixed DNA profiles where more than one person was a contributor.

By simplifying statistical reasoning, attorneys can prevent misinterpretations that could sway a verdict.

4. Leverage Expert Testimony Effectively

Forensic DNA analysts play a critical role in explaining evidence. Attorneys should:

Prepare Questions that Guide the Jury: Rather than asking experts to recite technical reports, structure testimony around clear, engaging explanations.
Anticipate Cross-Examination Tactics: Be ready to clarify potential counterarguments such as contamination risks or partial DNA profiles.

A confident and articulate DNA expert can add significant credibility to the prosecution or defense.

5. Address and Preempt Common Arguments (For Both Defense and Prosecution)

Regardless of whether you are defending or prosecuting a case, DNA evidence can be contested. Anticipating and addressing common challenges proactively can strengthen your argument. Consider the following points:

Chain of Custody: Ensure clear documentation of evidence handling to establish that the DNA was not contaminated or otherwise altered. This helps counter any claims about mishandling or improper storage of the evidence.
Mixture Interpretation: If the DNA sample contains contributions from multiple individuals, explain how analysts differentiate and interpret the various contributors. This can clarify the reliability of the results, whether for inclusion or exclusion.
Secondary Transfer: Address concerns about the possibility of DNA being transferred indirectly, which could weaken its evidentiary value. This explanation can help the jury understand how DNA may be transferred between people and objects.
Testing Limitations: Be transparent about the scope of the DNA results. For example, if the testing cannot determine the time of deposit, make sure jurors are aware of this limitation to avoid overstatements of certainty.

Being clear about the limitations and strengths of the evidence is key to presenting a compelling case.

Real-World Impact

Forensic DNA testing has led to both exonerations and convictions in high-profile cases. Clear communication of DNA evidence has been a deciding factor in cases such as:

Cold Case Solves: Advances in DNA technology have identified perpetrators decades after crimes were committed.
Wrongful Conviction Exonerations: DNA evidence has freed innocent individuals who were wrongly accused.
Serial Offender Identification: CODIS database matches have linked criminals across multiple states.

The ability to present DNA evidence effectively has real consequences—not just for individual cases, but for public trust in the justice system.

Strengthen Your DNA Case with Expert Support

DNA evidence is one of the most powerful tools in the courtroom—but only if jurors understand it. By utilizing visual storytelling, simplifying complex concepts, and preparing expert testimony effectively, attorneys can maximize the impact of forensic DNA results.