What Is Scientific Evidence?.
Scientific evidence is most often presented in court by an expert witness testifying on expert opinions. It also includes expert testimony that goes beyond science. The scientific expert is frequently called upon to interpret results and draw conclusions about what results mean in the case being tried.
Forensic Scientists rely primarily on scientific knowledge. However, only half the job is performed in the laboratory while the other half takes place in the courtroom.
These functions fit into three categories:
PHYSICAL EVIDENCE IS LESS LIKELY TO BE COMPROMISED OR TAINTED BY HUMAN EMOTIONS THAN EYEWITNESS ACCOUNTS FROM VICTIMS OR WITNESSES OR
THE ANALYSIS OF PHYSICAL EVIDENCE INVOLVES ADHERENCE TO STRICT GUIDELINES, SYSTEMATIC COLLECTION, ORGANIZATION AND ANALYSIS OF INFORMATION (THE SCIENTIFIC METHOD)
AN UNDERSTANDING OF THE ADMISSIBILITY OF EVIDENCE IS IMPORTANT.
Forensic Scientist are called on to evaluate evidence when the court lacks the expertise to do so
Must establish competency by citing educational degrees, number of years of occupational experience membership in professional societies, special courses taken and any professional articles or books published.
Cross-examination may reveal weaknesses in background and knowledge
Demeanor and ability to explain scientific data clearly and logically to a judge and jury of non-scientists
Must be an advocate of truth and not take a side
Evidence must be properly recognized, collected and preserved if it is to have value.
Many, but not all crime laboratories keep trained “evidence technicians”.
Sometimes a patrol officer or detective collects the evidence.
All officers engaged in fieldwork must be familiar with evidence collection.
These people are trained by laboratory staff through extensive personal contact, lectures, laboratory tours and/or dissemination of manuals.
How does the court decide whether or not to accept scientific evidence? The judge and jury are typically not scientifically trained.
Several court cases illustrate the steps in the development of admissibility.
Scientific validity of polygraph is rejected
Court ruled that in order to be admitted as evidence in trial the questioned procedure, technique or procedure must be “generally accepted” by a meaningful segment of the scientific community.
Collection of experts called in to testify about the validity of scientific issues
Books and papers written on subject reviewed and discussed.
A code of evidence law governing the admissibility of evidence in the U.S. federal court system enacted in 1975.
Rule 702 applies to scientific, technical or otherwise specialized knowledge.
Individual states are free to adopt different evidence rules but most have codes that are based on FRYE.
Where an expert witness testifies to an opinion based on a new or novel scientific methodology or principle, the proponent of the opinion has the burden of showing the methodology or scientific principle on which the opinion is based is sufficiently established to have gained general acceptance in the particular field in which it belongs.
“general acceptance” or Frye standard no longer absolute prerequisite.
Trial judge given the task of ensuring an expert testimony rests on a reliable foundation, is relevant to case, and is not repetitive, inflammatory or unnecessarily confusing. (gatekeeper)
Whether the scientific technique or theory can be (and has been) tested.
Whether the technique or theory has been subject to peer review & publication
The technique’s potential rate of error
The existence and maintenance of standards
Whether the scientific theory or method has attracted widespread acceptance within a relevant scientific community
Different methods-same results: “Frye in drag”