Forensic Science and the Law

Forensic Scientist Ethics As with other witnesses, forensic scientists obliged to tell the truth. Must attempt to state facts without distortion Omission of relevant information (statistics) Allowing incorrect inferences to be made A witness’s expertise allows them to properly present the evidence.

Law > Forensic Science Ethics Bad: Sherlock Holmes type witness that makes conclusions without considering other possible explanations. Makes an impressive witness, but can unfairly influence jury.

Identical scientific results can be presented differently in court. Law > Forensic Science Ethics Identical scientific results can be presented differently in court. Must avoid being overly definitive or overly inconclusive.

“The gunshot was fired at a distance of 48.2 cm from the victim.” Law > Forensic Science Ethics Example: “The gunshot was fired at a distance of 48.2 cm from the victim.” Problem: This is overly specific. We know that it is not possible to measure the distance that accurately.

“The gun appeared to be 2.2 meters from the wall.” Law > Forensic Science Ethics Example: “The gun appeared to be 2.2 meters from the wall.” Problem: This is overly inconclusive. If it was measured to be 2.2 meters, just say that.

Evidence generated through science is called forensic evidence. Law > Forensic Evidence Evidence generated through science is called forensic evidence. Forensic evidence is circumstantial evidence. Finding a suspect’s blood at a crime scene implies the suspect was also at the crime scene.

Evidence left at crime scene Evidence collected by investigators Law > Forensic Evidence The amount of evidence that makes it into court is a portion of the total evidence. Evidence left at crime scene Evidence collected by investigators Evidence that can be tested and produces results Evidence allowed into court according to rules of evidence

Admissibility of Evidence Law > Forensic Evidence Admissibility of Evidence In order for scientific evidence to be useful, the method must be reliable. Three slightly varied tests are used to determine admissibility.

Admissibility of Evidence Law > Forensic Evidence Admissibility of Evidence Frye test (1923) Is the scientific theory generally accepted in the scientific community? Is the scientific method used generally accepted in the scientific community? Has the technique been applied correctly?

Admissibility of Evidence Law > Forensic Evidence Admissibility of Evidence Daubert test (1993) Has the scientific theory or technique been tested? Has the scientific theory or technique been subjected to peer review and publication? What are the known or potential error rates of the theory or technique when applied?

Admissibility of Evidence Law > Forensic Evidence Admissibility of Evidence Daubert test (1993) Do standards and controls exist and are they maintained? Has the theory or technique been generally accepted in the relevant scientific community?

Admissibility of Evidence Law > Forensic Evidence Admissibility of Evidence Revised Rule 702 If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case.

Polygraph