The Concept of Admissibility

Forensic science is the application of scientific theories and methodology to practical problems, particularly legal issues or disputes. The forum for resolution of a legal issue is a trial, in which a judge presides as the source of law and a jury of citizens decides the facts. An “expert” witness can give opinion testimony to assist the jury. Testimony from scientific experts is the classic form of expert testimony. Admissibility simply means that the judge will decide whether the jury should hear and consider some particular evidence. Generally, evidence that tends to prove or disprove guilt or innocence should be heard. But sometimes, while some evidence may tend to prove guilt or innocence, it still may be too prejudicial for a jury to consider. The judge is the “gatekeeper” and must determine what evidence is admissible. As to expert witnesses, the judge must decide if the jury needs an expert to help them understand the issue, if the expert is offering relevant and reliable testimony that will provide proof of guilt or innocence, and whether the expert is qualified to give the testimony.