Fingerprints and Impressions Questions and Answers

Answer: C

AFIS is a computerized system for storing and retrieving fingerprint records.

The Automated Fingerprint Identification System converts fingerprint images into digital records of their minutiae (ridge endings, bifurcations and their positions and directions). A print from a scene or a new arrest is searched against the database, and the system returns a ranked list of candidate matches, which an examiner then compares and confirms by eye.

AFIS does not estimate the age of a latent print, which no routine method does reliably. Tracking evidence through the chain of custody is done by laboratory information management systems, and hair is examined by microscopy, not by AFIS.

Answer: C

Bertillonage was mainly based on anthropometry.

Alphonse Bertillon of the Paris police introduced his system in 1882. It recorded a set of body measurements that were thought not to change in adult life, such as height, the length and breadth of the head, the length of the middle finger and of the foot, and the span of the arms. Prisoners were filed by these measurements, supplemented by a description and a standard photograph (the mug shot).

Photographs and descriptions were secondary parts of the system. Handwriting played no part, and fingerprints replaced Bertillonage in the early twentieth century, notably after the Will West case of 1903.

Answer: C

Dusty footwear impressions are best recovered by electrostatic lifting.

A dust print is a two-dimensional impression of loose dust on a surface such as a floor or a sheet of paper. An electrostatic dust print lifter lays a metallised film over the print and charges it, and the dust particles are attracted to the film, transferring the impression without disturbing it. The lifted print is then photographed under oblique light.

Plaster, dental stone, wax and sulphur casting are for three-dimensional impressions in soil, sand or snow. Poured on a dust print they would destroy it.

Answer: C

The popular material is liquid silicone rubber.

Striation marks, such as those left by a tool blade, are very fine scratches. Silicone rubber casting compounds (Mikrosil is a common one) flow into the finest detail, set quickly at room temperature, release cleanly from the surface without damaging it, and do not shrink, so the cast can be compared with test marks under a comparison microscope.

Plaster of Paris and dental plaster are for large three-dimensional impressions such as footwear and tyre marks and do not reproduce microscopic striations. Sulphur is used for casting impressions in snow and is too coarse for tool-mark detail.

Answer: A

Wear markings are not a class characteristic.

Class characteristics are features shared by every tyre of the same make and model: the tread design, the number and arrangement of the ribs (lands) and grooves, and their widths. They narrow the search to a type of tyre but cannot identify one tyre.

Wear is acquired in use. The way a particular tyre wears, together with cuts, embedded stones and repairs, is unique to it, so wear markings are individual (accidental) characteristics, the kind that can link an impression to one specific tyre. The other three options all describe the tyre's design, so they are class characteristics.

Answer: C

The measurement that cannot identify the manufacturer is the type of body built on the chassis.

From tyre tracks at a scene, investigators can measure the wheel base (the distance between front and rear axles) and the front and rear track widths (the distance between the wheels on an axle). These dimensions are fixed by the vehicle's design and can be compared with manufacturers' specifications to narrow down the make and model.

The type of body built on a chassis, such as a truck chassis carrying a tanker or a bus body, is often added by a separate body builder and leaves no trace in the tyre marks, so it cannot point to the manufacturer.

Answer: D

All four can be used, so the answer is I, II, III and IV.

Casting preserves three-dimensional impressions such as footprints, tyre marks and tool marks. Plaster of Paris and dental stone are the standard materials for impressions in soil. Silicone rubber casting compounds record fine detail in tool marks and on small surfaces. Moulage, a reversible gelatine-based material, and wax (or sulphur) are also used, for example for impressions in snow or on delicate surfaces.

The options leaving out plaster of Paris omit the most common casting material of all, and the others omit materials that are genuinely used.

Answer: A

The key's answer is the expansion factor.

Both ordinary plaster of Paris and dental plaster (dental stone) are calcium sulphate hemihydrate that sets by the same reaction, taking up water to form gypsum. Dental stone is made from denser, more regular crystals, so it needs less water, sets harder and stronger, and shows a smaller and more controlled setting expansion. That controlled expansion is why it gives more accurate casts of footwear impressions.

The chemical reaction is the same for both, so that option is wrong. Drying time and cost differ only incidentally and are not the defining difference.

Answer: C

Ted Bundy was convicted on bite mark evidence.

At his 1979 trial in Florida for the murders at the Chi Omega sorority house, the key physical evidence was a bite mark on the body of Lisa Levy. Forensic odontologists matched it to casts of Bundy's distinctive, uneven teeth, and the testimony was decisive in his conviction. The case is a landmark in the history of forensic odontology.

Bundy's convictions did not rest on latent fingerprints or blood evidence, and DNA profiling was not yet in forensic use in 1979.

Answer: C

The footwear outsole database is SICAR.

SICAR (Shoeprint Image Capture And Retrieval) stores and searches shoe sole patterns, so that a print from a scene can be linked to a make and model of footwear and to prints from other scenes.

AFIS is the Automated Fingerprint Identification System and CODIS the FBI's Combined DNA Index System. CHEMPLAST is not a forensic database at all. None of these holds outsole patterns.