Last Updated on: 20th October 2023, 09:48 am

How Can a Federal Defense Lawyer Challenge Forensic Evidence?

When a defendant is facing federal criminal charges, the prosecution will often rely heavily on forensic evidence to try to prove their case. This may include DNA evidence, ballistics analysis, fingerprint evidence, digital forensics from cell phones and computers, and more. As a federal defense lawyer, one of your key jobs is to scrutinize this forensic evidence and look for ways to challenge it if you believe it is flawed, inconclusive, misleading, or improperly collected and analyzed.

Here are some of the main strategies and methods criminal defense attorneys use to challenge questionable forensic evidence in federal cases:

File a Motion to Suppress

If you can show the forensic evidence was obtained illegally or in violation of the defendant’s constitutional rights, you can file a motion to suppress that evidence so it cannot be used at trial. For example, if the police searched your client’s home or electronic devices without a valid warrant and obtained forensic evidence like DNA or digital files, you can argue that evidence should be excluded under the exclusionary rule because it is “fruit of the poisonous tree.”

Retest Evidence Yourself

For scientific and technical forensic evidence like DNA samples or ballistics analysis, you may be able to independently re-test the evidence yourself using your own experts. If your experts reach different conclusions than the prosecution’s, this can undermine the reliability of the evidence and give jurors reasonable doubt.

Challenge the Collection Process

You can argue the forensic evidence was contaminated or improperly collected by police and analysts. For example, with DNA evidence you can scrutinize whether proper protocols were followed to avoid cross-contamination of samples. Or with digital evidence, you can look for gaps in the chain of custody.

Question the Analyst’s Credibility

Dig into the background, credentials, and track record of the forensic analysts who produced the evidence. Look for lack of certification, previous mistakes, or credibility issues that could make the jury doubt the reliability of their conclusions.

Highlight Lack of Context

Forensic evidence like DNA or partial fingerprints may only show your client was present at a location, not necessarily that they committed a crime. Argue the evidence lacks the context to directly link your client to criminal activity.

Challenge Statistical Interpretations

When analysts rely on statistics like random match probabilities for DNA, challenge their accuracy and highlight how statistics can be misinterpreted. For example, a DNA match may be extremely rare in the general population but more common among close relatives.

Argue Evidence Was Improperly Analyzed

Carefully scrutinize the methods used by analysts to highlight any flaws, inaccuracies, unsupported assumptions, or logical gaps. Consult experts to identify issues with their approach. For example, with ballistics you could argue they failed to account for certain factors affecting bullet markings.

Point to Exculpatory Evidence

Analyze the forensic evidence to identify any exculpatory findings that support your client’s innocence. For example, partial DNA from another person mixed with your client’s could raise reasonable doubt about their guilt.

Question Relevance of Evidence

The forensic evidence may be scientifically valid but still irrelevant to the legal questions before the jury. For example, trace DNA could have been transferred innocently through secondary transfer rather than directly at the crime scene.

Develop an Alternative Theory

Provide the jury with an alternative plausible explanation for the forensic evidence that does not involve your client’s guilt. For example, the presence of their DNA could be due to prior lawful access rather than illegal activity.

Highlight Lack of Other Evidence

Point out to the jury the lack of motives, witnesses, documents or other evidence corroborating the prosecution’s forensic evidence. Argue it does not tell the whole story.

Use Expert Witnesses

Retain qualified expert witnesses in the relevant fields to critically analyze the forensic evidence and testify about flaws in the analysis, conclusions, and collection methods. Their testimony can undermine the prosecution’s evidence.

Educate the Jury

Many types of forensic evidence rely on complex scientific analysis methods that juries may not fully grasp. Educate the jury through evidence and expert testimony about the limitations and pitfalls of pattern evidence, statistics, laboratory procedures, cognitive bias, and other issues so they view the evidence more critically.

Point to Past Errors

For established forensic techniques like bite mark analysis, highlight past cases where similar evidence led to wrongful convictions. This demonstrates fallibility.

Question Laboratory Accreditation

Verify that the laboratories involved were properly accredited and complied with quality assurance standards. Bring up any past quality control issues or questionable practices.

Request Access to Lab Data and Notes

Dig deeper by requesting access to all the laboratory’s bench notes, measurement data, and other information related to the analysis under discovery rules. Look for inconsistencies or omissions.

Get Evidence Examined by Defense Experts

Have defense experts examine key physical evidence like weapons or digital devices rather than relying solely on prosecution reports. Independent analysis may yield new information favorable to the defense.

Challenge the Significance of Results

With techniques like DNA mixture interpretation, highlight how subjective judgment calls about what alleles to include or exclude can dramatically affect the results and conclusions.

Allege Bias or Suggestiveness

Argue that forensic analysts were influenced by bias, pressure from investigators, or other factors that skewed their subjective interpretations and conclusions in favor of the prosecution’s case theory.

Call for Increased Scientific Scrutiny

For forensic evidence based on new or largely untested techniques, argue jurors should be highly skeptical absent more extensive scientific research, validation, and peer review in the community.

Compare Error Rates

Contrast the error rates of established forensic techniques like latent fingerprint analysis with the DNA analysis being presented, and argue jurors should demand stronger scientific proof.

Critique Population Statistics

Challenge the accuracy and relevance of random match probabilities and population statistics used with DNA evidence. Argue they do not necessarily apply to the subgroup relevant to your case.

Highlight Improper Extrapolations

Point out when analysts have overreached or drawn unsupported conclusions from the actual forensic findings. For example, claiming a hair “matches” the defendant even though hairs lack unique identifiers.

Attack Overstated Conclusions

Scrutinize the language analysts use, and challenge any statements asserting absolutes like “to a scientific certainty” or “zero error rate.” These types of overstated conclusions are rarely justified.

By employing the right combination of these strategies, a skilled federal defense lawyer can often successfully pick apart flawed forensic evidence and prevent it from being used improperly against their client. Thorough investigation, consulting experts, educating jurors, and capitalizing on any weaknesses or errors are key to challenging dubious forensic science.

References

Here are the references used in this article:

Justice Department Guidelines for Forensic Evidence

Attacking Forensic Evidence Handbook

Prosecutor’s Duty to Disclose Exculpatory Evidence

ABA Standards for DNA Evidence

Challenging Forensics: Verifying Chain of Custody