DNA evidence is frequently introduced as a pivotal part of the prosecution's case in many criminal cases, such as rape and murder. However, it’s crucial to understand that because your DNA allegedly matches that found at a crime scene, it doesn’t automatically lead to your conviction. Our experienced Manassas criminal defense lawyers at The Wilson Law Firm have the knowledge to challenge the DNA evidence being used against you and to mount an aggressive defense strategy to fight the criminal charges you face. 

What is DNA? DNA evidence sample tubes and bags

DNA, or deoxyribonucleic acid, is the fundamental genetic material present in nearly all living organisms. It serves as a unique blueprint for each individual, containing the genetic code that determines your physical characteristics, including eye color, hair type, and susceptibility to certain diseases. 

In a criminal context, DNA evidence is typically gathered from various sources, such as blood, hair, or bodily fluids, and then analyzed to establish a link between a suspect and a crime scene. 

Three Types of DNA Test Results

DNA testing has three main types of results, each with distinct implications. These results play a pivotal role in determining the strength or weakness of the evidence presented in a criminal case.


This means the DNA sample taken from a suspect is included as a possible source of the DNA discovered at the crime scene. It suggests there’s a significant likelihood that the suspect was present when the crime was committed.

However, inclusion doesn’t mean the accused's DNA matches the DNA collected at the crime scene. Thus, it doesn’t definitively prove guilt, as there may be legitimate reasons for the presence of an individual’s DNA at a location, or a defendant’s criminal defense attorneys can raise other challenges to the test results. 


Exclusion indicates the DNA sample taken from the suspect is inconsistent with DNA recovered from the crime scene. In this situation, the person would be excluded as a donor of the DNA evidence. 

This result is a powerful defense tool, as it casts doubt on the involvement of the accused at the crime scene. However, it doesn’t prove the defendant's innocence. Law enforcement officials may have collected other evidence they can use to try to prove the individual's guilt. 


An inconclusive result implies the DNA analysis couldn’t determine a conclusive match or exclusion. This might be due to factors such as degraded or contaminated samples, making it challenging to draw clear conclusions.

How DNA Evidence Is Used in Virginia Criminal Cases 

DNA evidence is primarily collected in felony cases in Virginia. It’s a powerful tool that can be used by the prosecution to try to convict someone and by a knowledgeable criminal defense attorney to prove a person's innocence. This evidence can also be utilized to identify a victim of a crime.

Virginia Code § 19.2-270.5 outlines the admissibility of DNA evidence in criminal proceedings, and it also sets forth the duty to notify the opposing party when planning to use DNA evidence.

This statute establishes that DNA testing is considered a reliable scientific technique, and the evidence derived from a DNA profile comparison can be admitted to prove or disprove the identity of any person. 

However, it doesn’t limit the introduction of any other relevant evidence that bears upon the questions at issue, including the accuracy and reliability of the procedures used in collecting and analyzing DNA samples.

Additionally, the statute mandates that the party intending to offer DNA evidence must provide written notice to the opposing party at least 21 days before the proceeding, along with copies of the profiles and the report or statement to be introduced. Failure to provide this notice might result in the court allowing the opposing party a continuance or, under certain circumstances, barring counsel from presenting such evidence.

How to Challenge DNA Evidence in a Virginia Criminal Case

Challenging DNA results can be a vital aspect of your defense strategy if you believe the evidence against you is flawed, unreliable, or that you were falsely accused of committing the crime

Here are several ways the skilled criminal defense lawyers at The Wilson Law Firm may be able to challenge DNA results and file a motion to suppress this evidence.

Insufficient Sample

A small or degraded DNA sample can yield inconclusive results. These can be challenged by questioning the adequacy of the sample and whether it provides a reliable basis for identification. You may need expert testimony to support the argument.

Contaminated Sample

Contamination can occur during the collection, handling, or testing of DNA samples. The crime scene sample could have been mixed with another one, or environmental factors—such as too high heat or moisture—can increase the tested sample's degradation. Your criminal defense attorney can challenge the results by demonstrating that the sample was tainted and untrustworthy.

Chain of Custody

Maintaining an unbroken chain of custody is essential to ensuring the integrity of DNA evidence.

Any lapses in the chain of custody from the moment the DNA sample was collected to its presentation in court can raise doubts about the reliability of the evidence, which you can use to contest the DNA results. 

Unreliability of Testing

DNA testing methods vary in reliability, and laboratories may use different procedures. Your defense team may raise questions about the results by examining the laboratory's methods, equipment, and the technicians' qualifications. Any deviations from established standards or doubts about the accuracy of the testing can be used to undermine the credibility of the evidence.