Fingerprints and Impressions Questions and Answers

Answer: B

The ABFO No. 2 scale is used in cases of bite marks.

The American Board of Forensic Odontology developed the ABFO No. 2 scale, an L-shaped rigid ruler with millimetre markings, circles for checking distortion, and grey bars for colour and exposure reference. It is placed in the same plane as a bite mark when it is photographed, so that the image can be corrected for size, angle and colour, and the mark compared accurately with a suspect's dentition.

Although the scale can be used for other patterned injuries, it was designed for and is identified with bite mark photography. Tool marks, fingerprints and bullet marks are recorded with other scales and methods.

Answer: B

Ninhydrin is triketohydrindene hydrate.

Ninhydrin (2,2-dihydroxyindane-1,3-dione) is the hydrate of indane-1,2,3-trione, traditionally named triketohydrindene hydrate. It reacts with amino acids in latent fingerprint residues on porous surfaces such as paper to give a purple product, Ruhemann's purple, and is one of the most widely used fingerprint reagents.

Hydroquinone is a photographic developer, the tetramethyl compound in the third option is not ninhydrin, and osmium tetroxide (printed 'trioxide') is a fuming reagent of a different kind.

Answer: A

Plaster of Paris cannot be used directly in snow because of its exothermic nature.

When plaster of Paris (calcium sulphate hemihydrate) is mixed with water it sets by an exothermic reaction, releasing heat as it hydrates to gypsum. Poured into a footprint or tyre track in snow, that heat melts the snow and destroys the detail of the impression.

Snow impressions are therefore first sprayed with a protective layer such as Snow Print Wax, and casts are made with dental stone mixed with cold water, or with sulphur, which melts at a low temperature. Cost, setting time and expansion are secondary concerns compared with melting the impression.

Answer: B

The distance between the centres of the front and rear wheels is the wheel base.

The wheelbase is measured between the centres of the front and rear axles on the same side of a vehicle. In accident reconstruction and tyre-mark analysis, it helps to identify the vehicle type from tracks and to reconstruct turning paths, since it fixes the geometry of turning circles.

The distance between the centres of the left and right wheels on the same axle is the track width, section width is the width of a single tyre, and 'wheel distance' is not a standard term.

Answer: C

Edgeoscopy was developed by Salil K. Chatterjee.

In 1962 Salil Kumar Chatterjee of India proposed edgeoscopy, the study of the shapes of the edges of friction ridges, such as straight, convex, peak, table, pocket, concave and angle forms, as an additional means of fingerprint identification when only small fragments are available. It belongs to the third level of ridge detail, together with poroscopy.

Edmond Locard developed poroscopy, the study of sweat pores, in 1912. E.R. Henry devised the Henry classification system with Azizul Haque and Hem Chandra Bose, and Cummins and Midlo founded dermatoglyphics.

Answer: C

Iodine fuming develops latent prints in a yellowish-brown colour.

Iodine crystals sublime on gentle heating, and the vapour is absorbed by the oily and fatty components of a fingerprint residue, staining the print yellowish brown. The method is non-destructive and suits porous surfaces like paper, but the colour fades quickly as the iodine sublimes away, so the prints must be photographed at once or fixed, for example with starch or alpha-naphthoflavone, which turns them blue-black.

Purple is the colour of ninhydrin-developed prints (Ruhemann's purple), and black is typical of powders or silver nitrate after exposure to light.

Answer: B

The key's answer is 2 mm. I could not confirm the figure in a source, so this follows the key.

Battley's single-digit system, a method for filing and searching a single fingerprint in a collection, used a special reticle (lens) with concentric circles to mark out the areas of the print that are examined for core, delta and ridge counts, as a technical note of the US National Bureau of Standards describes it. The distance between consecutive circles is the radial step of that reticle.

The same note gives spacings only for other systems: parallel lines 6 mm apart in the Collins system and 4 mm apart in the Jorgensen system. Those are not Battley's, so 4 mm should not be chosen by borrowing it. The 1, 3 and 4 mm options could not be ruled out from a source either.

Answer: C

The uniqueness of the iris lies in its random textural variations.

The iris has a complex texture of crypts, furrows, freckles, rings and the collarette that forms randomly during foetal development and is stable from early childhood. John Daugman's iris recognition algorithm encodes this texture as an 'iris code' from phase information, and the chance of two different irises matching is extremely small, even between the left and right eyes of the same person or between identical twins.

Colour and pigmentation are genetically determined and shared by many people, and the overall shape of the iris is similar in everyone, so neither gives uniqueness.

Answer: B

The marks made by lateral movement between two surfaces are striation marks.

In tool mark and firearm examination, sliding or scraping contact between a harder surface and a softer one leaves a pattern of fine parallel lines (striae) reflecting the microscopic irregularities of the tool's edge. Examples are the marks of a knife or bolt cutter, and the land and groove marks left on a bullet by the rifling of the barrel. Striations are compared under a comparison microscope.

Compression (impressed) marks are made when a tool is pressed into a surface without sliding, as with a hammer face or a firing pin. 'Lateral marks' and 'friction marks' are not the standard terms.

Answer: A

A cast made of a shoeprint in mud is a positive replica of the impression.

The impression in the mud is a negative, a mirror image of the sole in reverse relief. Filling it with dental stone or plaster produces a cast that reproduces the sole itself, with its tread pattern and wear standing up as on the shoe, which is why it is called a positive.

It is not a negative replica (that is the impression), and casts are made to be the same size as the shoe, not larger, apart from slight distortions of the soil.