The Assessment of Circumstantial Scientific Evidence

THE current trend toward the increased use of scientific evidence, in minor as well as in major cases, suggests that it is not out of place at the present time to review some of the problems that arise in the use of this type of evidence. Although circumstantial scientific evidence can never take the place of what may be called "ordinary" police evidence, it is, however, likely to be employed with increasing frequency as the knowledge of the possibilities of scientific aids in detection spreads. The establishment of scientific laboratories by certain country and city police forces, together with lectures and demonstrations, is helping to foster the growth of this knowledge. This knowledge must be put into practice primarily by detective officers themselves, and it is only by the development on their part of judgment in the selection of exhibits, which presupposes a knowledge of the possibilities of scientific aids, that the police laboratories will be able to operate with success. Only in exceptional cases is it likely that a scientific expert, or an officer specially trained in scientific methods, will be able himself to collect at the site of a crime the material for examination; in the majority of cases the laboratory will be dependent on the judgment of the officer in charge of the case for the collection of the exhibits. It will be evident that this officer should, and probably will, at any rate in