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Crime Scene Photography
Photography is used by the police to provide evidence and supplement written reports on a very extensive scale. Much of this work is of a routine character and not connected with the actual investigation of crime. The equipment and techniques employed in this branch are those of normal photography. Most of such photography is done "in the field".
Apart from such general work, however, there is the highly specialized field of photography applied to crime detection. Much of this is carried on in the laboratory with special equipment and techniques. By the use of such technical aids as infra-red and ultra-violet lighting, and radiography, in conjunction with suitable filters and sensitized materials, criminal evidence that would otherwise remain hidden can often be brought to light.
The work of the laboratory carries on from where the outdoor photographer leaves off, so there is inevitably a certain amount of overlapping in the work of the two departments.
In presenting photographs as evidence, the pictures must not be retouched (or even spotted) in any way.
For lighting subjects in and out of doors he will have a supply of enclosed flash bulbs with, possibly, several high intensity Photoflood bulbs, reflectors and flexible leads and plugs. The special circumstances of this type of photography may call for fast, medium or slow orthochromatic or panchromatic films or plates.
In the police laboratory, the photographic equipment normally includes a long extension camera which can be fitted with short focus camera lenses to make low power photomicrographs up to about ten diameters. For greater magnification than this, the photographer may use any of the normal equipment for photomicrography. Finally, in addition to the usual lighting equipment (Photofloods, flash bulbs, and normal electric lighting units) there are special lamps for generating infra-red and ultra-violet light.
The infra-red light sources are used for such work as the examination of heavily dyed textile fibers, of sections of biological material where the natural pigment is reddish or brownish in color, and for showing up the presence of carbon on sections taken from the lung in cases of suffocation by smoke. Various inks, sealing waxes, seals, markings of stamps, etc., often yield positive evidence by the use of infra-red photomicrography. Ultra-violet lighting is extensively used for revealing forgeries and fakes. Many inks and pigments which are apparently identical by ordinary lighting fluoresce differently under ultra-violet lighting, and the difference can be photographed.
There is rarely any provision for making X-rays in the photographic department: when X-rays are required the work is done by independent specialist firms.
The ordinary police photographic department staffed by policemen photographers is concerned almost entirely with straightforward pictures of scenes of crime and personal identification. This makes up the overwhelming majority of photographic jobs in crime photography.
The Scene of the Crime
A typical outdoor job for the police photographer might be to take a number of exterior scenes of a house showing the point of entry of a criminal, of a field, wood or lane connected with a murder or sex offense, or a road showing the scene of an accident. Photographs are wanted here to show how the particular spot was approached, its visibility from the highway and its connexion with other points of evidence.
If the crime has been committed in a building it is usual to take several general views from different angles, using a wide angle lens in conjunction with Photoflood or flash bulbs, or using daylight, with or without artificial light of some sort, as illumination. Special attention is paid to recording the position of various objects with relation to the body (if there is one), the point of entry or exit of any intruder, etc. Care has to be taken when using the wide angle lens to avoid distortion caused by having the back of the camera out of vertical.
Close-ups of important details are generally desirable. For these and the more general shots the proprietary self-contained lighting units are very valuable. They not only ensure adequate and correct illumination, but also allow the operator the opportunity, which he does not get with flash, of examining the picture before exposure. This allows him to avoid "flares" and reflections from mirrors, polished fittings, glass, etc., in the final picture. Backed plates are normally preferable for interior work since they yield brighter and clearer negatives.
The use of available daylight brings in a number of minor complications, since its uncertain and fluctuating intensity and the often unsuitable position of windows make calculations of exposure rather rough and ready and may render it difficult to take an exposure in the direction required. These difficulties are overcome by obscuring windows with curtains and using artificial illumination only. On occasions this may be supplied by flash bulbs or powder.
In the latter case the lens is focused on an ordinary hand torch directed towards the camera from each side of the subject in turn. This also helps to define the limits of the picture.
Hans Gross, the authority on criminal investigation, lays down as an inviolable rule that one must "never alter the position of, or pick up, or even touch any object before it has been minutely described in the report". The value of the camera to make a record of the position of objects in relation to each other and to reproduce a likeness of an object, as it was when first found, thus becomes very obvious indeed.
Generally, the photographs considered essential are those showing the scene itself, any points of exit and entry, all points where traces of the crime are found or where they might have been expected but where, in fact, there are none, and the scene from spots where witnesses have seen, or could have seen, anything. A number of these points are often not apparent in the early stages of the investigation so that it is generally considered better to take too many rather than too few photographs. Views are, therefore, taken from several sides and angles, and reference points from which the photographs were taken are marked on a diagram of the scene. The diagram is also marked with measurements showing the space-relationship of various objects.
The photographs, beside being an impartial record of things present in their state when photographed, will also indicate things which should normally be there but are in fact absent. Sometimes such missing elements may lead to important deductions being made as to how, or by whom, the crime was committed.
In road accident cases, photographs are taken along the lines of approach of the two vehicles at the eye height of the sitting drivers in order to demonstrate their field of vision before the accident. Photographs are also taken of the actual scene and of any marks on the cars which may have special significance. There may be skid marks on the road, or, in the case of hit-and-run incidents, tire impressions on the victim's person. How these are photographed will depend upon the nature of the surface and the type of impression. A Polaroid screen may be used over the lens to reduce reflection from the road. Or again, the photographer may actually make use of the glare caused by oblique daylight to obtain better contrast, taking vertical photographs of the surface with the camera stopped down to less than f11, and a process film to give extreme contrast. If it is visible, the whole tire impression is recorded in the hope that, besides identifying the make of tire, the particular tire in question may show a characteristic marking or fault such as a peculiar cut, mark, etc.
Photographs for identification are taken in a studio with light-colored walls. Profile and full face photos of one-eighth scale, and full length photos of l/27th scale are taken on the fastest type of plate or film, with the lens at about the level of the sitter's face or chest height for the full length photograph. The focal length of the lens used is at least equal to the diameter of the picture in order to produce satisfactory perspective free from distortion of the features.
When recording diseased skin, bruises or injuries, use may be made of suitable filters and plates to obtain either faithful or deliberately exaggerated reproduction. By using an orthochromatic plate and no filter under artificial lighting, for instance, it is possible to show the extent of bruises not readily visible to the eye. They can be made even plainer by the use of color-insensitive plates.
"Candid" motion pictures are a valuable means of identification. Pictures taken of a man "off his guard" often reveal characteristic movements of hands, feet or head which can identify him as surely as a physical peculiarity. X-ray photographs of teeth and other portions of the anatomy, preserved in practitioners' records, have, on occasions, been produced for positive identification of living people and even more particularly for identifying cadavers. Identification after Death. It is possible to identify corpses even in such a state of advanced decomposition that the features are unrecognizable. For this the police need a photograph of the person when alive, for preference one of the full face. A life-size negative of the skull of the corpse is taken from the same angle as the existing photograph, and printed as a transparency. The existing photograph is then enlarged to life size and placed under the transparency and in register with it. The extent to which the eyes, ears and nose in the "living" photograph correspond to the sockets, the bony aperture and the nasal bones, respectively, in the transparency of the skull is noted. These observations will go a long way towards establishing whether the two photographs belong to one and the same person. If "living" photographs of the head in three different positions are available, the certainty of identification can be almost guaranteed.
High power photomicrography of occupational dusts (i.e., fragments of material found in a place where a man works) has often proved of importance in identification, or in connecting suspects with a crime.
Coal particles can be embedded in the skin of miners and remain for a number of years; certain classes of quarrymen are found to have tiny particles of silica in their breathing tracts and lungs. The presence of shellac in the system has been used to identify the body of a french polisher. Similarly, metal particles are associated with engineers, cereal and malt debris with brewery workers, and flour and starches with adhesive makers, bakers, millers, etc. There are many similar associations.
The pattern of the ridges on the finger tips is an unchanging characteristic of the individual. These ridges contain sweat glands, and pressure of the finger tip on a surface leaves an extremely fine film of grease in the characteristic pattern of the ridges. When the finger prints are dusted with an appropriate powder, the powder clings to the greasy parts and can be blown away from the rest of the area, leaving a finger print impression that is visible and can be photographed.
Suitably colored dusting powders are used to contrast with the color of the surfaces bearing the finger prints. Black powder is used for a white ground, white powder for a black ground. On colored grounds, a colored powder is used in conjunction with the plates and color filters that give the best contrast. On multi-colored backgrounds the photographer uses a powder which fluoresces in ultra-violet light to give a photograph in which the glowing finger prints are shown against a dull background.
The photographer's ingenuity is demonstrated at its best when finger prints occur in different places, for example, on both sides of a piece of glass. In this case the prints on one side are dusted with a light powder and photographed against a dark background, after which the prints on the reverse side are dusted with a black powder and photographed against a white background.
Prints in an inaccessible position may often be photographed by employing a mirror. In this case unbacked film loaded the wrong way round in the holder is used to counteract the reversal of the image by the mirror.
The police record finger prints by pressing the fingers first on to an inked pad and then on to a sheet of white paper, so that the ridges show as black lines on a white background— the reverse of the picture produced when white powdered or light-colored powdered finger prints are photographed against a dark background. For this reason the tones of the photograph must be reversed, but it must not be reversed laterally, i.e., from left to right. To do this a lateral reverse negative is prepared by taking a photograph on an unbacked plate or film, loaded back to front in the camera. From this an intermediate positive transparency is prepared. The positive is then printed in the usual way to obtain prints for comparison with the actual police records, the effect being that of a finger print made with black ink on white paper. For finger prints consisting of dark colored powder on a light background, a direct photographic method without reversal gives the required print for comparison.
There is a simpler method of correctly recording light powder finger prints on a dark ground. If the plate holder is loaded with bromide paper and the finger prints are photographed through a prism or optical mirror set up in front of the lens to correct the lateral reversal, developing and fixing in the usual way gives the desired print. But by this method only one print can be made for each exposure in the camera and any duplicate records must be made by repeating the whole process.
Another method preferred by a number of police departments for photographing light powder impressions is to expose on a thin fast film, and then develop, bleach, expose to white light, and redevelop. This gives a positive which can be printed in the normal way to give a black on white image with no lateral reversal.
For comparing finger print photographs, enlargements of about 6 diameters are used.
The skin on the finger tips of corpses is often hard and shriveled, making straightforward finger printing impossible. In such cases, the skin is stripped from the fingers, well massaged with a barium paste, mounted between glass plates and photographed with rear illumination and the lens stopped down to at least f45.
Police photography also includes an appreciable amount of foot print recording either in the form of dust prints on linoleum, etc., or impressions in earth, clay, or snow.
Examination of car tire marks also comes into this category.
Technically the photography is fairly straightforward. Oblique illumination is often used where practicable to show up impressions in relief.
Debris on the Person
Photomicrography at magnifications of the order of 200 x to 750 X is employed for the examination of fibers from clothing and other textiles, paper, hairs, dust and debris, which may be found in the turn-ups of trousers, in pockets, under the finger nails, and in the aural or nasal cavities.
In many instances the debris under the nails or in the turn-ups of the trousers has been obviously connected with the scene of a crime- e.g., fragments of pine needles have been found in the clothing of the murderer when the crime took place in a wood, and alum and wood fragments have been photographed on the clothing of a thief who had ripped open the fireproof lining of a safe.
Debris in Lungs
The lungs of a corpse often reveal significant traces of foreign matter that help in establishing the cause and time of death, and even of identity (when they contain characteristic occupational dusts). Thus in the examination of the lungs of a man who had died in a fire, sections of the lung tissue stained red with safranin and photographed through a red filter on panchromatic film clearly showed carbon deposits in the tissue. These deposits indicated that the man had inhaled smoke from the fire and therefore was alive before the fire had started.
The debris in the water of ponds, ditches, and streams is often characteristic, and, in the case of drowning, the water in the lungs should contain debris of a similar nature to that in the water in which it is presumed death occurred. Totally different debris present could indicate that the body had been taken away from the site of death, and put into the water in another place to divert suspicion and enquiries from the proper quarter. Debris present in the lungs, therefore, allows the real site of death to be sought and identified with accuracy.
Stains on Clothing
Bloodstains are such a vital form of evidence that many complex techniques have been developed to detect them on all types of surface and material. Photography in one form or another enters into all these methods of detection since a photograph is more convincing than a mere statement. But in many instances the evidence could not be revealed without the photographic process.
For instance, a colored fabric may be more transparent to infra-red rays than a bloodstain of the same color. Or the stain may have been caught in such a state that it is relatively opaque to the rays. In these circumstances the presence of otherwise invisible stains, their shape, and location, can be reproduced by infra-red photographic technique.
Blood, seminal stains, starches and occupational dusts of various types are also revealed by photomicrography which shows up the characteristic structure and color of the material; and by ultra-violet radiation which characterizes certain substances by their fluorescence. Alternatively, infra-red illumination may be used, in particular to reveal internal structural detail normally masked by a skin or covering that is relatively opaque to visible light.
In poisoning cases, particularly in tropical countries, the presence of certain vegetable poisons may sometimes be established by the presence of characteristic fragments of berries, leaves, stems or roots. Photomicrographs of such fragments assist the prosecution in explaining to the judge and jury reasons for identifying the material as the vegetable poison used. Various dried and ground insects, powdered glass, and finely chopped hair are other fairly common native poisons whose presence can be clearly shown in photomicrographs.
Firearms and Ammunition
Guns and bullets can usually be identified by the striations left on the bullets by the rifling of the weapon, the indentation left by the firing pin in the soft metal of the firing cap, the impression made on the base of the cartridge by being forced into contact with the gun breach by the pressure of the explosion, and the marks of the extractor and the ejector on the cartridges. Evidence of this type is photographed generally at magnifications of about 3 x to 6 x on slow or medium speed emulsions giving good or high contrast. The lighting is arranged to shine almost parallel to the surface so that it throws the indentation, scratches, etc., into bold relief. (This method is also used for examining markings on metal objects like coins, in forgery cases, and door locks, window hasps, etc., in "breaking and entering" cases).
Textiles may be examined for stains and powder marks from bullets, etc., under infrared light. The opaque carbon from the explosive blown from the muzzle of the firearm is deposited around the point of impact of the bullet according to certain well-known laws.
For instance, if these marks can be seen, as on a white fabric, it is possible to calculate the distance, etc., of the muzzle from the fabric at the time of firing. With colored fabrics, the location of this carbon deposit is not so easy to see, but when photographed by infra-red light the conformation of the carbon deposit can be clearly demonstrated, even on dark colored textiles. Where the bullet enters the body it generally leaves a ring of metal which can be seen in an X-ray photograph where the metal, being relatively opaque to the X-rays, shows up as a distinct image.
Forensic Photography: Importance of Accuracy
Crime Scene Photography
The Practical Methodology of Forensic Photography
Documents on which the writing has been obliterated by dirt or by the passage of time are regularly photographed by infra-red illumination to reveal the original writing. This is possible because infra-red light generally shows a higher penetrating power than visual light, and although it is invisible, infra-red light affects the emulsion of the special plates and produces a visible photographic image. Sometimes even charred documents can be made legible by this method provided the charring hasn't gone too far.
The same technique has also revealed alterations in passports, additions in different ink or with different pencil to documents, and it has often been successful in reproducing indecipherable drawings and sketches which have been obliterated by rubbing or other mechanical friction.
Since some inks are more opaque than others to infra-red rays, it has been possible to reproduce the hidden text in certain passages of old manuscripts which have been obliterated- e.g. by the censor of the Spanish Inquisition. More recently the method has been used to reveal the original document when dirt, inks, etc., have been deliberately applied in an endeavor to hide the underlying text. Writing. Questions of the authorship of handwriting are tackled by comparing low power photomicrographs of specimens. Negatives of individual letters enlarged from five to ten times can be superimposed to show similarities. The same type of test is used to establish typewritten text as the work of one particular machine. No two typewriters give identical impressions; there are always slight differences in the lining up of the type bars or even microscopic differences in the shape of the letters. All these points can be demonstrated with photographically enlarged reproductions. Photography by oblique light can also reveal the impression left on a pad after the top sheet with the writing on it has been torn off.