In many criminal cases, the prosecution relies heavily on expert witnesses to present scientific or technical opinions. These experts may testify about DNA evidence, ballistics, handwriting analysis, accident reconstruction, digital forensics, or other specialized areas.
Because juries tend to give significant weight to expert testimony, these opinions can carry more influence than almost any other type of evidence presented at trial. When an expert tells a jury that a bullet came from a particular gun or that DNA is a “match,” that conclusion is often viewed as definitive.
Experts are human. They rely on training, experience, and methods that may be flawed, outdated, or misapplied. In some cases, the “expert” may not be qualified in the specific area at issue. In others, the method used to reach a conclusion may not meet accepted scientific standards.
One of the most effective ways to challenge an expert witness is through a Daubert motion. An experienced criminal defense attorney like Andrew Stevenson knows how useful Daubert motions can be, and he’s ready to explore how one can help you in your criminal case.
A Daubert motion is a request for a pretrial hearing in which the court determines whether an expert witness should be permitted to testify. The motion is based on United States Supreme Court decisions, including Daubert v. Merrell Dow Pharmaceuticals and Kumho Tire Co. v. Carmichael, which established the framework for evaluating expert testimony.
At a Daubert hearing, the judge acts as a gatekeeper. Before the jury ever hears from the expert, the court must decide whether the testimony is both relevant and reliable.
Two primary questions are addressed:
If the answer to either question is no, the expert’s testimony may be excluded entirely. This makes a Daubert motion one of the most powerful tools available in defending a case involving expert evidence.
Expert witnesses are permitted to offer opinions that ordinary witnesses cannot. While a lay witness can describe what they saw or heard, an expert can interpret evidence and draw conclusions.
For example, an expert may testify that:
These opinions are often presented as scientific conclusions, and jurors may assume they are objective and unquestionable.
However, there are several reasons why expert testimony should be examined carefully:
In some cases, entire areas of forensic science have been questioned or criticized in recent years. Methods once widely accepted have been shown to have limitations or high error rates.
A successful Daubert challenge can prevent an expert from testifying altogether. Even when the challenge is not successful, it often exposes weaknesses that can be used effectively at trial.
The first area of focus in a Daubert hearing is the expert’s qualifications.
Courts often look at whether a witness has been previously accepted as an expert. However, prior qualification is not enough. Just because a witness has testified as an expert in other cases does not mean they are qualified in your case.
A proper evaluation should include:
For example, a person with a Ph.D. in chemistry may not be qualified to offer opinions on accident reconstruction or physics-based analysis. Similarly, someone with general forensic experience may not have the specialized knowledge required for a particular type of testing.
It is also important to look beyond credentials. An expert’s publications, research, and prior testimony can provide insight into their actual expertise. In some cases, an expert may rely more on courtroom appearances than on meaningful work in the field. Carefully examining these factors can reveal that the “expert” is not as qualified as they appear.
In many cases, the most effective challenge focuses on the method used by the expert rather than the expert themselves.
Courts evaluate methodology based on two key concepts:
A method can appear reliable but still be invalid. For example, a test might consistently produce results, but if there is no sound scientific basis for how it works, those results may not be meaningful.
Many forensic methods are based on research conducted years or even decades ago. While that research may have been accepted at the time, it may not reflect current technology or understanding.
It is often possible to identify:
For example, methods used to calculate speed from skid marks or analyze tool marks may rely on assumptions that no longer hold true for modern vehicles or equipment.
By examining the foundation of the method, it is possible to challenge whether it should be relied upon at all.
Challenging an expert requires more than legal knowledge. It requires an understanding of the subject itself.
Attorneys are often at a disadvantage when dealing with technical or scientific testimony. Taking the time to learn the basics of the field allows for a more effective challenge.
This preparation makes it possible to:
Being able to speak the same language as the expert is critical. Without that understanding, it is difficult to effectively challenge the testimony.
Many forensic methods include a portion of the process that is difficult to explain. This may involve complex calculations, specialized software, or machinery that even the expert does not fully understand.
This is often referred to as the “black box” of the method.
If an expert cannot clearly explain how a key part of the process works, it raises serious questions about the reliability of the results. Even if the court allows the testimony, this lack of clarity can be powerful in front of a jury.
Jurors are often skeptical of conclusions that cannot be explained in a straightforward way.
An independent expert can play an important role in challenging expert testimony.
Even if your expert cannot say that the method is entirely flawed, they can:
In many cases, an independent expert can help uncover issues that would not be apparent from the reports alone.
If a Daubert motion is successful, the expert will not be allowed to testify at trial.
This can have a significant impact on the case, particularly if the prosecution relied heavily on that testimony. Without the expert, key elements of the case may be weakened or unsupported.
In some situations, excluding an expert can lead to reduced charges or even dismissal.
If the challenge is not successful, the hearing still provides valuable information. It allows the defense to understand the expert’s opinions, methods, and weaknesses, which can then be used during cross-examination.
Challenging expert testimony requires a combination of legal skill and practical experience.
It involves:
Without a thorough approach, expert testimony may go unchallenged or be accepted at face value.
In cases where expert witnesses play a central role, having an attorney who understands both the legal standards and the underlying science is critical.
If your case involves expert testimony, the outcome may depend on how that evidence is handled.
Andrew H. Stevenson has extensive experience challenging forensic evidence and expert witnesses in criminal cases. By carefully examining both the qualifications of the expert and the methods used, he works to identify weaknesses and protect his clients’ rights.
To discuss your case, contact his office or call (740) 654-4998 today for a free consultation.