The Science of Defense: Challenging Forensic Evidence in Court 

Forensic evidence refers to the use of science to investigate crimes. It can be used to analyze “hard” evidence like hair and fingerprints. It can also be used to investigate or explain “soft” traits such as a person’s psychological profile. Today, most prosecutions rely on forensic science, such as DNA and blood spatter analysis.

Because forensic evidence is rooted in scientific research, jurors tend to believe it. While some forms of forensics are reliable, a growing number of studies are pointing out the flaws in many types of forensic science.

If you or a loved one has been charged with a crime,  understanding forensic evidence is a must. This post discusses the various types of forensic evidence, the problems with forensic evidence, and how a Marin County criminal defense attorney can help you challenge forensic evidence in your case.

Common Types of Forensic Evidence

After a crime is committed, specialized teams go to the scene to collect evidence such as body fluids, fingerprints, and fabrics. This evidence must be carefully collected and stored to prevent any damage. Additionally, the team must create and maintain a chain of custody. A chain of custody is a record that shows where the evidence was located at any given time. If someone wants to review the evidence, the log will show when it was removed from storage and who took it.

There are many types of forensic evidence. Some of the most common include:

• Ballistic evidence,
• Bite mark evidence,
• Blood spatter analysis,
• DNA evidence,
• Digital evidence (e.g., cell tower records)
• Fingerprint analysis,
• Footwear impressions,
• Tire impressions,
• Toxicology reports, and
• Trace evidence analysis. This science involves the testing of microscopic amounts of fibers, paint, soil, and other items.

Forensic evidence has many uses. For example, ballistics can be used to show the type of weapon that fired a bullet. DNA evidence is often used to show that a person was (or was not) at the crime scene. Trace evidence can be used to show that a person visited a particular location. The types and uses of forensic evidence are almost limitless.

Problems with Forensic Evidence 

Forensic science is not necessarily a bad thing. Defense attorneys have used DNA evidence to exonerate many wrongfully convicted people. However, no science is perfect. Here are five issues that experts have found with forensic evidence:

• Contamination. The chain of custody discussed above is very important. If there is a “break” in this chain – that is, if the evidence is removed and not accounted for – there is no way to know if the evidence was properly cared for during this time. Evidence that is improperly stored or handled could be exposed to contaminants. Biological materials such as DNA evidence are particularly susceptible to contamination.

• Crime Lab Testing Errors. Most lab errors relate to storage, contamination, or testing. As far as storage, blood and other types of biological evidence must be stored at specific temperatures. Failure to do so can damage them and affect any analysis. If lab workers don’t handle samples carefully, they could contaminate them. Underqualified or inexperienced lab personnel may make mistakes, misinterpret results, or use improper procedures. These errors can create false positives or make evidence unusable.

•  Examiner Bias. Some fields of forensics rely on interpretation. The results in these cases can change based on the examiner’s subjective views. For example, if evidence can be interpreted in more than one way, an examiner who believes that the accused is guilty is more likely to interpret the evidence in that way.

• Unreliable Science. The science behind some forms of forensics, such as DNA, is solid. Other types of forensics, such as polygraphs (lie detectors), are so unreliable that they are no longer admissible in court. Some, like fingerprint, blood spatter, and bite mark analysis, were once widely accepted but are now being reconsidered due to new research.

•  Expert Witness Misconduct. Expert witnesses can  purposefully exaggerate their findings to help prove someone’s guilt or, alternatively, describe findings that help the defense as “inconclusive.” While rare, studies report that prosecution experts have engaged in evidence tampering, lied about results, or even hidden evidence.

Fighting Back Against Forensic Errors

Forensic evidence can be flawed, but luckily, there are ways to correct the record. A Marin County criminal defense lawyer can help you. Your lawyer can:

• Challenge the science. Your lawyer can hire expert witnesses who can testify that the prosecution’s experts used outdated science and explain more recent findings.

• Challenge the expert. On cross-examination, your attorney can make the expert defend their education, their process, and their findings. If the expert is particularly unqualified, your lawyer may be able to convince the court to block their testimony.

• Discuss the chain of custody. Once your lawyer gets the prosecution’s witnesses to admit that the chain of custody was broken, the defense experts can explain how contamination could affect the results.

• Challenge the results. Your lawyer can send the evidence to an independent laboratory. Your experts can explain the different outcomes to the jury.

Get a Marin County Criminal Defense Lawyer to Help You Fight Bad Forensic Evidence

Good forensic evidence can prove someone’s innocence, but bad forensic science can lead to a wrongful conviction. To get a fair result at your trial, you’ll need to challenge the bad evidence or work to keep it out of court. An experienced Marin County criminal defense attorney can help. If you or a loved one has been charged with a crime, call Brownstein Law Group. We specialize in helping people fight DUI arrests and other serious charges. If you need a Marin County DUI attorney or legal representation for other minor or serious crimes, we can help. Our lawyers have over 40 years of combined experience. We know how to challenge flawed forensic science in court, and we are always willing to go the extra mile to get the best results for our clients. Contact us today to learn more about how we can help you protect your freedom.