Abstract

The uses of various optical methods in forensic science are briefly reviewed—in particular, visual examination, microscopy, x-rays and photography, x-ray diffraction, spectrophotometry, emission spectrography, and neutron activation analysis. Attention is directed to some recent developments, particularly in the methods of bloodstain examination.

© 1969 Optical Society of America

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Figures (7)

Fig. 1
Fig. 1

The value of visual comparison. Two old women were knocked down and killed by a hit-and-run car. In the subsequent examination of a suspected vehicle, parts of the front nearside suspension wishbone were found to have been rubbed free of grease and dirt. A heel of one of the dead women’s shoes bore indentations reproducing the shapes of parts in question. Photograph of heel: British Crown Copyright. Permission of Director of Publications, H. M. Stationery Office. Photograph of wishbone: Copyright and Courtesy, Chief Constable of South Shields, County Durham, England.

Fig. 2
Fig. 2

A comparison microscope: A— prism housing; B—eyepiece; C—objectives on rotating turrets; D—objects under examination (bullets in this case); E—object stages; and Flight sources.

Fig. 3
Fig. 3

Comparison of striations. Several hundred dollars’ worth of brass turnings was stolen from an engineering shop, and a few days later a ton of such turnings was sold to a scrap metal dealer. Information given by the dealer to the police led to the arrest of two men, from the clothing of whom there were recovered some fragmentary brass turnings of the same composition as the stolen brass. These, and turnings from the scene of the theft, were also found when examined together under a comparison microscope to bear matching striations, showing that both sets of turnings had been turned at about the same time with the same tool. British Crown Copyright. Permission of Director of Publications, H. M. Stationery Office. Courtesy of Director, Home Office Forensic Science Laboratory, Bristol, England.

Fig. 4
Fig. 4

Differentiation using uv reflectivity. These photographs are of marks made on grey paper with white pigments—titanium oxide (wavy line) and zinc oxide (ellipse). A is a straight photograph by visible light; B a photograph by uv (approximately 360–400 mμ).

Fig. 5
Fig. 5

Ultraviolet spectrophotometry is used routinely in forensic science for the preliminary identification of many drugs. It is particularly useful with the barbiturates, since the absorptions of these compounds show a very characteristic dependence upon pH. With the common di-substituted barbituric acids—e.g., amylobarbital—set of curves (a), the peak which appears at approximately 238 mμ at pH 10 (ammonium hydroxide solution) moves to approximately 251 mμ at pH 13 (sodium hydroxide solution). With the less common N-substituted barbituric acids, e.g., methohexitone sodium, 1-methyl-5-allyl-5-(1-methyl-2-pentenyl)—barbituric acid—set of curves (b), the corresponding peak changes very little with alkalinity, since these compounds cannot become doubly ionized. All curves read at a concentration of 20 μg/ml.

Fig. 6
Fig. 6

Infrared spectrophotometry is particularly useful in forensic science in the characterization of involatile organic materials of indefinite or complicated chemical composition. For example, the identification of greases or heavy-duty lubricating oils may be important in cases of larceny or where these substances occur as contact traces, e.g., in cases of felonious entry into machine shops or of the theft of oily machine parts. On the basis of the three curves for oil samples shown here, it is obvious that (a) and (b) may well have a common origin, but that (c) is quite different.

Fig. 7
Fig. 7

Spectrographic analysis. A color photography processing works in the London area was burgled. The continuous handling of photographic materials had led in course of time to the soil around the works containing a detectable trace of silver—an element not normally present in London soils. An arrested man had mud on his shoes and in his light truck. This was compared spectrographically with the soil from around the works. (a) Reference iron spectrum. (b) Typical soil from another part of London. (c) Soil from beside the burgled premises. (d) Mud from suspect’s shoes. (e) Mud from suspect’s truck. (f) R.U. powder. Note the absence of silver from (b), but its presence in (c), (d), and (e). Courtesy and copyright, Commissioner of Police of the Metropolis London.

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