Federal Rule of Evidence (FRE) 702 is crucial for forensic expert testimony because the trial judge acts as a gatekeeper who determines whether the proposed expert evidence is sufficiently reliable and relevant before being presented to the jury. There is an emphasis in the amendment of FRE 702 that is especially relevant to the expert testimony of forensic service providers:
- Helpfulness: the expert’s specialized knowledge will help the factfinder understand evidence or determine a fact in issue
- Adequate basis: the opinion is based on sufficient facts or data
- Reliable methodology: the testimony is the product of reliable principles and methods
- Reliability of application: the expert has reliably applied those principles and methods to the facts of the particular case
Why does this matter for forensic science?
During the qualification process, the forensic expert may be asked a series of qualifying questions regarding knowledge, skills, experience, training, and education. Once qualified, the forensic expert should be capable of explaining the procedures performed during testing of the evidence and the results provided in the report. The explanation of the results need not exceed what the underlying data, methodology, validation, and application can support.
How should forensic experts prepare?
Document qualifications on a curriculum vitae (CV)
- education and specialized training
- certifications or professional credentials
- publications and presentations
- experience with the particular methodology
- continuing education
Know the scientific foundation of the methodology
The expert should be able to articulate:
- the methodology procedure and how it works
- limit of detection, specificity, and sensitivity of the methodology
- reproducibility and concordance of the methodology
- appropriate quality controls
- relevant peer-reviewed literature pertaining to methodology
- acceptance of methodology within the scientific community
Be prepared to defend the actual application
The expert should specifically identify:
- the items of evidence examined
- the observations made at time of testing
- the interpretation process
- overall technical and administrative peer review process
Testify within the scope of the field
Forensic experts should be particularly cognizant during their testimony to not mislead, overvalue, or undervalue the evidence. For example, DNA analysts should be familiar with the limitations of the transfer, persistence, prevalence, and recovery (TPPR) of DNA. Therefore, when asked questions pertaining to how or when the DNA was deposited (or lack thereof), the DNA analyst should iterate that answering would be outside the purview of their testimony and a separate evaluation would be needed to address those specific questions.
Be familiar with chain of custody
The chain of custody is a chronological record tracking the movement of evidence and must be maintained by all laboratories with access to the evidence. This prevents the substitution, tampering, damaging, altering, contamination, misplacement, or falsification of the evidence; thereby, maintaining the legal integrity of the evidence. Failure to establish the identification, authentication, legal integrity, and completion of the chain of custody may result in the exclusion of evidence or limitations to the jury relating to the weight of the expert testimony.
Conclusion
Under FRE 702, a forensic expert should be able explain the scientific foundation and application of the methodology, identify specific items of evidence, demonstrate the completeness of the chain of custody, and testify within the scope of the field. In addition, the expert should be cognizant of the limitations of what the scientific method reliably supports.
Resources:
https://www.law.cornell.edu/rules/fre/rule_702
R221b- Annex B- Specific Requirements- A2LA Texas Forensic Science Commission Crime Laboratory Accreditation Program