Effect of Water on FDR

It has been observed that in casework involving examination of damp or wet clothing for FDR, the success rate was very low (such clothing would be dried before sampling). Possible explanations are that the particles are chemically attacked by water, that the water removes the particles by physical disturbance, for example, washed away by rain, that the water moves the particles farther into the fabric of the garment and the sampling procedure fails to recover them, or that all the cases submitted just happen to be negative. Laboratory experience and casework details make the last two options unlikely. In an attempt to clarify the situation several tests were conducted. The first test involved sampling of the firing hand immediately after firing using the same swabbing material but three different solvents, two of which had water added to them. Results are presented in Table 20.4.

Given the random nature of FDR deposition and particle recovery there is insufficient evidence to draw any conclusions from this test, although the presence of water does not appear to have a noticeable detrimental effect.

table 20.4 Effect of Water in the swabbing solvent

Solvent

Particles Detected

Petroleum ether

Acetone-water

Acetonitrile-water

11 x Pb, Sb, Ba; 3 x Sb, Ba; 34 x Pb, Sb; 3 x Pb, Ba 58 x Pb, Sb, Ba; 46 x Pb, Sb; 4 x Pb, Ba 6 x Pb, Sb, Ba; 8 x Pb, Sb

The next test involved the distribution of lead in FDR between two solvents, namely, petroleum ether and water, in an attempt to determine the effect of water on the level of lead in FDR; lead was chosen because it is present in FDR at a much higher level than either antimony or barium. Separation funnels on a vibration-free surface were used for the test. Before use, both the petroleum ether and deionized water were analyzed for lead with negative result. The results are given in Table 20.5.

Again, there is insufficient evidence to draw conclusions, and the test results are difficult to explain. The lost lead from the petroleum ether layer could have been adsorbed on to the surface of the separating funnel and/or concentrated at the petroleum ether/water interface. A small amount of lead did enter the water layer in tests 2 and 3 but none in test 1. This could be due to a small proportion of the discharge residue containing a water-soluble lead compound or a small number of insoluble lead-containing particles finding their way into suspension in the water layer.

A further test involved repeatedly treating a sample with water prior to carbon coating for manual SEM/EDX examination, with a duplicate, untreated sample acting as a control. When examined, both samples had a high concentration of particles encompassing the complete range of particle types. The sample treated with water did not show any noticeable difference.

There is nothing to indicate that water has a significant chemical effect on the particles. It is likely that water, in the form of rain, would substantially decrease particle population by physical disturbance.

table 20.5 Lead Distribution Between Layers

Sample

Test No.

Initial (ng)

48 Hours (ng)

Difference (ng)

Petroleum

1

2,700

1,900

800

Ether

2

1,900

275

1,625

Layer

3

4,025

3,750

275

Water

1

None

None

None

Layer

2

None

100

100

3

None

50

50

Casework-Related Tests Bullet Fragmentation

As a result of a terrorist attack on a motor vehicle, in which the terrorists used 7.62 mm x 39 mm caliber Yugoslavian nny 82 ammunition, the driver was shot dead. A large number of bullets struck the car, and the interior of the car and the clothing of the deceased suffered severe bullet fragmentation damage. An item of clothing worn by the deceased was examined for FDR, not as a requirement of the case but to gain background knowledge of the types of particles originating from bullet fragmentation.

Examination revealed that the sample contained both spherical and irregular particles, although the vast majority of particles were spherical. The spherical particles could originate from the considerable heat generated when a high velocity bullet strikes a hard surface, such as vehicle glass or bodywork.196

Numerous lead, antimony particles were detected accompanied by copper, zinc particles, iron particles, and lead-only particles. The lead, antimony; copper, zinc; and lead-only particles, probably originated from the bullets and the iron particles probably originated from the car bodywork. No unique FDR particles or other FDR particle types were detected.

If required to examine a person for FDR who had been subjected to bullet fragmentation, the presence of such large numbers of particles originating from fragmentation would make the task very difficult. In this instance no unique FDR particles were detected. However, it is possible that all types of FDR particles could be carried on the surface of the bullets, and this possibility would have to be carefully considered in this type of examination.

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