Trace Evidence Examination Questions and Answers

Answer: C

The most suitable combination for the density gradient column is bromoform and bromobenzene, option C. In the density gradient tube method for comparing soil or glass, two miscible liquids of different density are used, so that the column has a smooth gradient from the lighter liquid at the top to the heavier at the bottom, and the particles settle at the level of their own density. Bromoform is dense and bromobenzene is lighter, and they mix freely. The combinations with phenol (A, D) or methanol (B) are not accepted by the key as suitable pairs for the column.

Answer: C

The angle of application of the tool should be considered for making standard tool marks with a screwdriver, option C. A screwdriver leaves a mark that depends strongly on the angle at which the blade is held against the surface, so test marks must be made at a number of angles to be compared with the questioned mark. A hammer (A) leaves an impression of its face, pliers (B) leave marks of the jaws and a prybar (D) leaves a mark of its blade; the key treats the angle of application as essential for the screwdriver.

Answer: D

Nodes are seen in the linen fibre, option D. Linen is made from flax, a bast fibre whose long cells show cross markings called nodes, or joints, along the length, which help to identify it under the microscope. Cotton (A) has a flat twisted ribbon form, wool (B) has surface scales, and silk (C) is a smooth structureless fibre, and none of them has nodes. Wool is recognised by the overlapping scales on its surface, and cotton by the flat twisted ribbon with a central lumen.

Answer: B

The 4-R rule is connected with glass fracture, option B. The rule says that radial cracks make a right angle on the rear side, which means that they form a right angle at the side of the glass opposite the side on which force was applied, so the direction of a blow or a bullet can be told from the cracks. It is not linked with arson (A), fibre (C) or soil (D).

Answer: B

A crater shaped hole in glass is narrower on the side where the projectile entered the glass, option B. The hole made by a bullet is conical, because the glass chips away from the exit side, so the opening is wider on the side from which the projectile leaves. This allows the direction of fire to be determined from the shape of the hole. The hole is not similar on both sides (A), and the wider side is the exit side (C), not the entry side. The shape of the crater is used to decide the direction of a projectile hitting a window pane: the cone opens in the direction in which the projectile was travelling.

Answer: D

All three are considered parts of the gait pattern, so the answer is option D. The step length is the distance between successive footprints of opposite feet, the foot angle is the angle at which the foot is turned out from the line of walking, and the walking line is the line along which the steps are taken. Since each of A, B and C is a component of gait, the combined option is right. The study of gait is used in forensic work to link a trail of footprints to a person, since the walking pattern is personal.

Answer: A

Black mineral colours in soil are generally related to the presence of manganese and iron, option A. Manganese oxides give black or dark brown colours to soils and iron compounds add dark shades, which is why these elements are used to explain dark coloured soil in forensic comparison. Copper minerals (B) are usually green or blue, chromium minerals (C) are green, and iron phosphate minerals (D) are bluish or whitish. Brown and red colours in soil are most often due to iron oxides.