Criminal cases today are often decided on forensic evidence. DNA analysis, toxicology, digital data, and other scientific methods are routinely presented as objective proof of guilt. Jurors tend to trust this evidence, especially when it is explained by expert witnesses and supported by lab reports.
That trust can be misplaced.
Forensic evidence is not immune to error, bias, or misinterpretation. It is collected by people, tested by people, and explained by people. Each step introduces the potential for mistakes. When those mistakes go unchallenged, they can have serious consequences.
A strong criminal defense requires more than reviewing reports and accepting conclusions. It requires a working understanding of the science, the methods behind it, and the limitations that are often overlooked in court. Defending your freedom and your rights requires working with a skilled defense attorney like Andrew Stevenson. Call IFBYPHONE to schedule your consultation to learn more today.
For many defendants, the most important part of their case is not what they say, but what the evidence appears to show. Prosecutors know this and often build their case around forensic findings that sound definitive.
Jurors, in turn, are conditioned to believe that scientific evidence is neutral and conclusive. Television and media coverage have reinforced the idea that forensic results are precise and reliable. This has led to what is often referred to as the “CSI effect,” where jurors expect scientific proof and give it significant weight when it is presented.
In reality, forensic evidence is rarely as straightforward as it appears.
Every forensic conclusion depends on:
Each of these steps can introduce uncertainty. In some cases, those uncertainties are minor. In others, they can fundamentally undermine the reliability of the evidence.
Careful, methodical review of forensic evidence often reveals issues that are not obvious on the surface. Those issues can become the basis for challenging the prosecution’s case and establishing reasonable doubt.
Forensic evidence covers a wide range of scientific disciplines. While each type of evidence is presented as objective, all of them depend on proper procedures and accurate interpretation.
DNA evidence is often viewed as the most powerful form of forensic evidence. It can be used to exclude individuals as contributors to biological material found at a scene, and in some cases, it can suggest that a person may have contributed to that material.
However, DNA evidence is more complex than it appears. Issues can arise with mixed samples, where DNA from multiple individuals is present, making interpretation more difficult. Low-level or “touch DNA” can be transferred through indirect contact, raising questions about how the material was deposited.
Contamination during collection or testing can also affect results. Even when testing is performed correctly, conclusions are expressed in probabilities, not certainty.
Fingerprint evidence is commonly used to connect a person to an object or location. While it is often presented as reliable, it depends heavily on the quality of the print, the method of collection, and the interpretation of the analyst.
Partial or smudged prints can lead to subjective comparisons. In some cases, different analysts may reach different conclusions based on the same evidence. Errors in fingerprint identification, while not common, do occur and can have serious consequences.
Toxicology testing is frequently used in OVI, DUI, and other criminal cases to determine the presence and concentration of substances in a person’s system.
These tests must be conducted and interpreted carefully. Blood alcohol levels can change over time, and the timing of a test relative to driving or an alleged offense can be critical. Improper handling of samples, delays in testing, or issues with calibration of testing equipment can all affect the accuracy of results.
Gas chromatography-mass spectrometry is widely used in drug cases to identify substances and determine their composition. While it is considered a reliable method, it is not immune to error.
False positives can occur if testing procedures are not followed correctly. Lab conditions, contamination, and analyst error can all impact the results. In some cases, the interpretation of data can be as important as the testing itself.
Bloodstain pattern analysis is used to reconstruct events based on the location and characteristics of blood at a scene, found at particularly violent crime scenes like murder or domestic violence. It is often presented as a way to determine how an incident occurred.
This type of evidence can be highly subjective. Conclusions depend on assumptions about how blood behaves under certain conditions, and those assumptions are not always accurate. Disagreements between experts are not uncommon, particularly in complex cases.
DNA evidence is a powerful tool, but it is frequently misunderstood by jurors and overstated in court.
The most important concept to understand is that DNA analysis is strongest when it excludes a person, not when it includes them. If a DNA profile does not match a suspect, that individual can be ruled out. When a profile appears to match, the result is expressed as a probability, not a certainty.
Even in cases where the statistical probability is extremely high, DNA evidence has important limitations.
Additional complications arise in cases involving low copy number DNA or mixed samples. When very small amounts of DNA are analyzed, the risk of error increases. When multiple contributors are present, interpretation becomes more complex and less certain.
Understanding these limitations is essential. Without that understanding, DNA evidence can be given more weight than it deserves.
Forensic evidence does not stand on its own. It is the product of a process, and that process must be examined at every stage.
The reliability of forensic evidence begins at the scene. If evidence is collected improperly, contaminated, or mislabeled, those issues can affect everything that follows.
Proper procedures must be followed to ensure that evidence is preserved in its original condition. When those procedures are not followed, the integrity of the evidence can be compromised.
Once evidence is collected, it must be tracked and documented. The chain of custody is intended to show who handled the evidence and how it was stored at each stage.
Breakdowns in this process can raise questions about whether the evidence was altered, contaminated, or even mixed up with other samples.
Testing must be conducted using properly maintained equipment and validated methods. Labs must follow strict protocols, and analysts must be properly trained.
Errors can occur due to equipment issues, contamination, or deviations from established procedures. In some cases, backlogs and time pressures can contribute to mistakes.
Even when testing is performed correctly, the results must be interpreted. This is where subjectivity can enter the process.
Analysts may draw conclusions that go beyond what the data actually supports. In some cases, there may be a tendency to interpret results in a way that aligns with the prosecution’s theory of the case.
Forensic evidence is often presented through expert witnesses. These individuals are expected to explain complex scientific concepts to a jury.
The credibility and qualifications of these experts matter. Their methods, assumptions, and conclusions must be examined carefully. Cross-examination can reveal weaknesses, inconsistencies, or overstatements that affect how the evidence is perceived.
Understanding forensic evidence requires more than familiarity with reports. It requires the ability to analyze scientific methods, identify weaknesses, and challenge conclusions effectively.
Andrew H. Stevenson has more than 25 years of experience in criminal defense and holds a Ph.D. in criminology. His background includes extensive work with forensic evidence in cases involving serious criminal charges, including violent offenses, sex crimes, drug cases, and OVI matters.
Rather than accepting forensic conclusions at face value, he examines how the evidence was developed, whether proper procedures were followed, and whether the conclusions are supported by the underlying data.
A successful defense requires attention to detail and a willingness to challenge assumptions.
By working with private investigators and independent forensic experts, Andrew H. Stevenson takes a comprehensive approach to analyzing evidence. Each case is evaluated on its own facts, and each piece of evidence is scrutinized for accuracy and reliability.
If there are errors, inconsistencies, or unsupported conclusions, they are identified and addressed.
If you are facing criminal charges, the forensic evidence in your case may play a central role in the outcome. Understanding that evidence and knowing how to challenge it can make a significant difference.
Andrew H. Stevenson offers free initial consultations and represents clients from offices in Athens and Lancaster, Ohio. Call (740) 654-4998 or use his contact form to start your defense today.