Because the work of a forensic scientist is intended to be used in court and because scientific evidence can be very powerful, the forensic scientist must be accurate, methodical, detailed, and above all, unbiased. The ability to keep detailed notes and to write clear, concise, and accurate reports is vital.
The forensic scientist must be able to determine which facts or items of evidence are relevant. In most cases, that’s easy – the item or items are provided to the forensic scientist for examination and analysis. In other cases, the forensic scientist may need (or want) to personally go to the scene to conduct an on-site analysis, gather evidence, or document facts for later analysis. Having been provided or having gathered the relevant information, the forensic scientist then has to decide which examinations, tests, or analyses are appropriate – and relevant – to the issue(s) in dispute. (Is that powder cocaine or not? Did a defect in the road surface cause the crash?). Then, the forensic scientist must conduct the most appropriate tests/analyses and document the process. Afterward, the forensic scientist must interpret the results and write a clear, concise report documenting the steps followed to reach this conclusion or opinion of the forensic scientist.
The forensic scientist will, at some point, have to testify. Testimony is the verbal statement of a witness, under oath, to the judge or jury. Forensic scientists are “expert” witnesses as opposed to ordinary or “fact” witnesses. Expert witnesses are permitted to testify not just about what the results of testing or analysis were (“facts”), but also to give an opinion about what those results mean. For example, a forensic scientist may testify about the observed, factual results of a chemical drug analysis and that, in their expert opinion, the results show that the tested substance is a specific drug, such as cocaine or heroin.
To qualify as an expert witness, the forensic scientist must have a solid, documented background of education, training, and experience in the scientific discipline used to conduct the examinations, testing, or analyses about which the forensic scientist wants to testify.
Sometimes in court, the work or qualifications of the forensic scientist are challenged. A party to a court case may challenge whether the scientist performed the tests correctly; whether the scientist interpreted the results accurately; or, whether the underlying science is valid and reliable. Finally, a party to a court case may challenge whether the scientist is properly qualified to render an expert opinion or question the scientist’s impartiality.
“If the law has made you a witness, remain a man of science. You have no victim to avenge, no guilty or innocent person to convict or save — you must bear testimony within the limits of science.”
— Dr. P.C.H. Brouardel
19th-Century French Medico-Legalist