Understanding DNA Evidence, Its Use in Minnesota Courts, and the Defense Role

Forensic DNA evidence is a tool that scientists use to help solve crimes. DNA is sometimes called a genetic blueprint because it contains all of the instructions that determine an individual’s genetic characteristics. DNA evidence plays a critical role in criminal prosecutions and criminal defense.

At Birkholz Law in Mankato, Minnesota, our criminal defense attorneys understand both the science behind DNA and the legal strategies needed to challenge or contextualize it in court.
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What is DNA Evidence?

DNA stands for deoxyribonucleic acid. It is the genetic material present in almost every cell of the human body and contains a unique profile for each individual (except identical twins). Humans share about 99.9% of the same DNA. There are, however, places on the human DNA molecule where humans can differ. Just like the English alphabet only has a limited number of letters to make up different letter combinations to form words; DNA also has a limited number of base pair combinations that can be used throughout all humans to create the human genetic markers. Typically speaking, with DNA we get half of our DNA from our mom and half of our DNA from our dad. Which means at each location we will typically have one genetic marker from mom and one genetic marker from dad.

For legal and forensic purposes, the idea is that biological specimens collected at a crime scene — for example blood, semen, saliva, skin cells — may contain DNA that can be compared to a suspect’s DNA sample. A person’s DNA is the same in blood, saliva, hair, semen, skin cells and other biological material. Biological material may be present at a crime scene even if it is not visible to the naked eye.

During the early decades of forensic DNA analysis, an evidence sample containing thousands of cells, such as a visible blood or semen stain, was needed to produce a DNA profile. Today, analysts can extract a DNA profile from a few skin cells that someone might leave behind.

DNA is comprised of four building blocks called bases or base pairs. The building blocks are: Cytosine, Guanine, Thymine, Adenine. These are commonly referred to as C, G, T, A. The pairing of these four building blocks always follow certain rules. Bases can only pair together in a specific way: C only bonds to G, and T only bonds to A. Which means you can have C-G, G-C, T-A and A-T.

It is the order (sequence) of these building blocks that determines each person’s genetic characteristics. All of the DNA in a cell is known as the genome. The human genome has approximately 3 billion base pairs.

The structure of DNA is like a ladder with the base pairs forming the rungs of the ladder. The entire ladder is twisted upon itself like a spiral staircase to form the double helix. Forensic scientists look at many specific regions on the DNA double helix. Each of those regions has several base pairs (rungs). The variation of genotype at multiple specific locations on the DNA is the foundation of forensic identity testing.

Why DNA Evidence Can be so Powerful

The 0.01% of DNA that is not the same between all humans is highly individualized. Single source DNA samples (DNA coming from only one person) have long been referred to as “the gold standard.” T.V. shows have sensationalized forensic testing leaving the general public with a belief that it is reliable and bulletproof.

Judges, jurors, and often lawyers do not understand the science behind DNA testing and put an unreasonable amount of faith in the interpretations made by labs who are run by state law enforcement agencies.  However, despite its strength, DNA evidence is not infallible. In December 2024 the DNA Mixture Interpretation: A NIST Scientific Foundation Review was published bu the National Institute of Standards and Technology, a division of the U.S. Department of Commerce, and  states:

All scientific methods have limits. To use a method appropriately, one must understand those limits, which are inevitably tied to the risk one is willing to accept either as an individual or as a society. This is especially important in forensic science, as critical decisions impacting life and liberty are often based on the results of forensic analysis.

Use of DNA Evidence in Minnesota Courts: From Prosecution to Defense

DNA was first introduced as evidence in 1986 in a case from Leicester, England. It ultimately led to the conviction of Colin Pitchfork for the death of two teenage girls. Tommie Lee Andrews became the first offender to be criminally convicted in the United States in 1987 with the use of DNA evidence. DNA was first used in a criminal case in Minnesota in the early 1990’s.

Prosecution Use

For prosecutors in Minnesota, the benefit of DNA evidence is obvious. A prosecutor will typically try to introduce DNA evidence to link a suspect to crime-scene biological material, especially in crimes such as sexual assault, homicide, or violent assault. But this may also include crimes like felon in possession, theft, or burglary. Because the Minnesota statute allows DNA analysis results to be admissible without the need for an expert to first testify about the reliability of DNA analysis, it becomes imperative to have a defense attorney who knows how to raise an issue if there is concern with the reliability of testing in a particular case.

The Role of a Defense Attorney in DNA Evidence Cases

When handling cases in Minnesota courts that involve DNA evidence—the role of a defense attorney is multi-faceted:

1. Pre‐trial investigation of DNA evidence
   • Examine how the biological specimen was collected: Was chain of custody followed? Were there opportunities for contamination or degradation?
   • Was the sample appropriate? For example, was it victim vs suspect? Was the sample so degraded or mixed that the reliability is questionable?
   • Review the lab procedures: Did the lab follow its standardized procedures? Were the lab procedures based on foundationally reliable data?
   • Request discovery of DNA reports, lab notes, chain of custody, quality control records, interpretation methodology, statistical calculations, and any proficiency testing or accreditation records.
2. Challenging admissibility & interpretation
   • While Minnesota statute allows DNA results to be admissible without the need for an expert to establish the method’s general reliability, that does not mean every result is unassailable. The defense may challenge whether the particular test was performed properly, whether contamination occurred, whether the sample was degraded, or whether proper reference samples were compared. Under the Minnesota Rules of Evidence a defense attorney can challenge the foundational reliability of a specific sample in a particular case.
   • Challenge statistical probability evidence under § 634.26: sometimes the phrasing of “one in x million” may mislead jurors. Defence attorneys must ensure clarity and context (e.g., population database used, relevant sub‐population, mixture interpretation).
   • In some instances the defense may seek independent testing be done or that an outside expert review the work done by a lab if there are questions regarding the reliability of a particular test or interpretation.
3. Presenting alternative explanations
   • The defense can review all the evidence in the case, consult with the suspect to find viable explanations other than guilt, which can explain the DNA evidence.
   • The defense can seek its own independent expert to find alternative explanations if the scientific work which was performed is not reliable.

What to Do If You’re Facing DNA Evidence in a Minnesota Case

In Minnesota, DNA testing itself has been found to be reliable and accepted by the general scientific community. Under Minnesota Statute, the analysis of those testing results are presumed to be admissible, unless challenged. What this means from a practical standpoint is that fighting DNA in a case will typically focus on the reliability of a particular test rather than the general acceptance of DNA testing.

Why A Specialized DNA Defense Attorney Matters

When DNA evidence is involved, the stakes are higher and the technical complexity increases. A defense attorney familiar with DNA issues in Minnesota courts can make a crucial difference. Here’s why:

• Technical expertise: A DNA defense attorney knows the forensic science, understands lab reports, chain of custody, statistical probabilities, mixture interpretation and how to hire independent experts when needed.
• Strategic defense: They can develop a defense strategy specifically tailored to the DNA evidence — whether that is challenging the evidence, negotiating regarding it, or using it proactively.
• Procedural understanding: They understand Minnesota discovery rules, how to obtain forensic discovery, when to seek independent testing, and how to handle motions to suppress DNA evidence.
• Client counselling: They guide clients through complex issues such as what challenges may be relevant to their case, how jury perception works, and risks/benefits of plea versus trial in the face of DNA evidence and any specific limitations of the DNA testing in their case.
• Mitigation and negotiation: If DNA evidence is strong, a defense attorney may still secure better outcomes (reduced sentence, alternative plea) by negotiating with an understanding of the DNA strength and weaknesses.

Practical Steps for Defendants in Minnesota Facing DNA Evidence

If you or a loved one are facing charges in Minnesota where DNA evidence is in play, here are practical steps to consider:

1. Retain a qualified DNA defense attorney: Don’t assume general criminal defense experience alone is enough. Look for someone with experience handling DNA cases in Minnesota courts.
2. Obtain full discovery early: This includes DNA reports, chain of custody documentation, lab accreditation details, mixture interpretation, statistical probability explanation, lab policies, laboratory unexpected results, lab audit information and any prior testing results.
3. Review the collection/handling: Was the specimen collected according to Minnesota law? Were proper protocols used? Were proper kits used? Was the chain of custody maintained? Was contamination possible?
4. Review the laboratory work: Which markers were tested? Was a mixture present? Were there any inhibitors? Was the lab accredited? Was there degradation in the sample? Was there a binary interpretation or was a probabilistic genotype software (such as STRmix) used? Were the lab’s policies and procedures followed?
5. Challenge or negotiate based on strengths/weaknesses: If the defense sees weaknesses (contamination risk, weak sample, mixture, partial match, etc), it may be possible to challenge or minimize the impact of the DNA evidence.
6. Consider independent testing or expert review: Even if the lab is the state’s lab, obtaining an independent review may reveal vulnerabilities or alternative explanations.
7. Prepare for jury understanding: DNA evidence is persuasive to juries but also technical. The defense must ensure experts explain DNA issues clearly and point out limitations.

Emerging Issues and Trends in Minnesota DNA Litigation

While the basic statutes are in place, there are evolving issues in Minnesota DNA practice that a DNA defense attorney must watch:

• Mixture interpretation: Many crime-scene samples contain DNA from multiple individuals. Interpretation of mixtures is more complex and more vulnerable to questionable interpretations and defense challenges.
• Secondary transfer and contamination: Defense counsel are increasingly raising issues of innocent transfer (someone else’s DNA being transferred to evidence) or contamination during collection/processing.
• Database and genealogical techniques: Some investigations use advanced techniques such as genetic genealogy. Defense attorneys need to monitor whether these are being used in Minnesota and whether constitutional or discovery issues apply.
• Backlogs and delays: As DNA testing becomes more in demand, delays in processing or backlog issues can affect the rights of defendants and timing of trials. This becomes important when deciding whether to file a speedy trial demand in your case.
• Technology improvements (not all are good): As forensic DNA technology improves (e.g., next-generation sequencing, low-copy number DNA, improved mixture deconvolution), what was once considered a reliable technique may now be subject to fresh challenge or reinterpretation. 

Need Help? Speak with a Minnesota Criminal Defense Attorney

DNA evidence is one of the most scientifically powerful tools in modern criminal law. In Minnesota the law provides strong support for its admissibility. As a defendant, it is critical to remember that DNA evidence is not automatic conviction material: it is technical, sometimes complex, and open to meaningful challenges by an experienced dense attorney.

If you or someone you know is facing criminal charges in Minnesota and DNA evidence is a factor, engaging an experienced DNA defense attorney should be a high priority. A skilled attorney will understand the nuances of Minnesota law, the lab’s protocols, and how to investigate, challenge or leverage DNA evidence to protect your rights.

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