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Fingerprints Found At The Scenes Of Crime (The following is from pages 105--109 of the 4th Edition of the book Classification and Uses of Finger Prints published in 1913 by His Majesty's Stationery Office, London, England. Thanks to Bill Leo--LASD for this contribution.) by SIR E.R. HENRY, G.C.V.O., K.C.B., C.S.I. Chief Inspector Charles Collins of the New Scotland Yard Finger Print Department, has prepared the following note which explains the method adopted in London:--— Evidence as to the identification of persons by means of finger prints, when given by competent witnesses, is accepted in Criminal Courts. Crime investigators should know the method by which finger prints are compared for the purpose of deciding questions of identity so that, with the aid of a reading glass, they can readily determine whether or not any particular impression possesses sufficient clearly defined characteristic detail for the purpose of fixing identity. Any article with a smooth surface is likely to retain imprints of value if touched. Finger prints on rough surfaces are, as a rule, of little use. Latent impressions can be developed with the aid of powders. If the marks are on blades of knives, plated goods, or on surfaces of a dark nature, “Grey” powder (mercury and chalk as sold commercially by chemists) is used. If the impressions are on paper or on surfaces of a light colour, graphite or lamp black will develop them. These powders ought to be used sparingly with a fine camel hair brush. All superfluous powder must be blown or brushed away. Unless the prints are latent, powder should not be used at the time of discovery by the Investigating Officer, as it sometimes happens that the powder reduces the area available for comparison by obscuring some of the characteristic detail. It is always possible for a skilful [sic] photographer to obtain a satisfactory photograph without the use of powder when the detail is discernible, though faint. When finger prints are on a part of a broken window, the remaining pieces should be preserved so that they might, if necessary, be fitted together, thus supplying evidence as to a particular piece being part of the window broken. Similar precaution should be taken in other instances if considered necessary. In all cases where finger prints are found at the scene of a crime, the Officer should endeavor to ascertain whether or not they are the prints of any person residing in the house, or those of a police officer or other person who may have arrived earlier on the scene. It should be distinctly understood that finger marks which do not disclose clearly defined detail when viewed through a reading glass are generally found to be useless when photographed. At New Scotland Yard much care and thought has been given to the photographing of finger marks, and as a result, efficient appliances have been installed. They include a large camera with sufficient bellows extension to enable prints to be enlarged six diameters, two powerful electric arc lamps which, by means of overhead rails, can be placed in any position; and an enlarging lantern capable of enlarging a finger print sixty diameters. Figure “A” illustrates the way in which finger perspiration marks on a piece of glass are photographed. The glass is placed between the jaws of a small vice. The vice has a fitting attached which permits of its sliding up or down a metal rod. The metal rod has a heavy base to keep it steady. A thumb screw is fitted so that the vice can be fixed to the rod at any height. A box about 18 inches deep of cross section 6 inches square, lined with black velvet, is placed on its side with the open end immediately behind the finger mark. The rays of light from the lamps are not permitted to reach the far end of the interior of the box, thus ensuring a dead black background. The lights (one on each side of the lens) are arranged in such position that the ridge lines when focused on the screen of the camera will appear light on a dark ground [ed--background]. This being the reverse of a finger print taken with ink on white paper, which is dark on a light ground, a second plate has to be made from the first by contact in the manner one would make a lantern plate. The printing is done from the second plate. The first plate when placed in the dark slide before it is exposed is reversed, that is to say the film side is away from the lens. If this is not done, when printing from the second plate, left will appear for right in the finished print, e.g. B appearing . Conversely, if the side of the glass on which the finger impression appears is turned away from the lens the first plate is not reversed.
Finger perspiration marks on blades of knives or on plated goods are photographed in a similar manner, but the velvet--lined box is not needed. The lighting is sometimes difficult since the article must be placed and lighted in such a way that the impression will appear on the screen light on a dark ground. A little patience is rewarded by obtaining the desired result.
Similar imprints on glass bottles and tumblers are photographed by the preceding method, but the bottles are filled with a black or dark red fluid to get the necessary contrast. Tumblers can be filled with a similar liquid when the marks are on the outside of the glass, but, as a rule, better results are obtained by placing a piece of dead black paper in contact with the whole of the inside surface of the vessel with the exception of that part covered by the finger print. Another sheet of this paper prevents light entering the top.
The convexity of bottles, etc., is sometimes the cause of reflections appearing over a part of the area covered by the finger impression. This is removed by altering the position of the lamps. When finger prints are found on the smooth side of corrugated glass, the numerous reflections are removed by filling the uneven surface with black printing ink. The ridges of fingers when impressed heavily on a candle create furrows similar in pattern to those of the ridges. Before being photographed such imprints are treated in the following manner:--—The impression is covered with printing ink, superfluous ink being afterwards removed until only that in the furrows remain. This is a similar process to that adopted by printers when preparing an engraved name plate for press.
Finger marks in blood or dark impressions on a light surface are photographed as if black on a white ground.
It sometimes happens that when a finger covered with a liquid such as blood is impressed heavily, the pattern left indicates that of the furrows, not the ridges. If on comparison this is found to be the case a photograph showing the true sequence can be obtained by reversing the first plate and making a second by contact.
Slow plates and a developer likely to produce maximum contrast should be used.
It is not possible to give definite information concerning the exposure of plates, so many factors have to be considered. When photographing a faint mark illuminated by two arc lamps with slow plates, F.22 stop and enlarging six diameters, twenty to thirty minutes exposure is given. It is not suggested that these hints cover the whole field of this interesting subject. Each case must be dealt with as occasion requires. It is thought, however, that they may assist those possessing a good knowledge of photography who are called upon to photograph finger marks found at the scenes of crime.
Figure “B” (not reprinted) illustrates the way in which fingerprint exhibits are prepared at New Scotland Yard for production in Court. The characteristics, such as bifurcations, abruptly terminating ridges, or any other noticeable peculiarities, are marked with red ink and numbered as shown. The exhibits are enlarged six diameters. A sufficient number , usually about twelve, are prepared for distribution amongst the judge, the jury, and counsel. A few unmarked copies are always available in case they might be required.
This article was reprinted in “THE PRINT” |