Packaging and Handling Evidence

Evidence and comparison samples to be submitted to a criminal investigation laboratory should be prepared using the following guidelines:

1. During the collection and packaging of evidence and samples, be careful not to mix any of the items of evidence with each other or with the comparison samples.

2. New or unused medical pillboxes or small cardboard containers with tight-fitting covers (similar to those used for packaging ice cream), sealed tightly with cellophane or other adhesive tape, are suitable for packaging dry soil samples. If the soil samples are wet they should be permitted to dry naturally in a dust-free room. Soil samples should not be dried by artificial heat.

3. Soil and rock evidence or comparison samples believed to contain petroleum or other volatile materials should be packed promptly into small mason-type jars with tight-fitting lids. The lids should be screwed on tightly and the edges sealed with wax.

4. Individual containers, marked for identification and sealed to prevent leakage or contamination, should be packed into a large substantial container for shipment to the laboratory.

5. Excelsior, cotton, or crumpled paper should be used to fill any vacant spaces in the package to provide additional protection for the individual samples.

Laboratory Examination

Given adequate samples that have been correctly collected and identified laboratory personnel may do the following:

1. Acertain whether two samples of rock or soil could have come from the same location. A more positive statement cannot be made, since it is possible, though not likely, that samples from two different places may be identical.

2. Determine that two specimens of soil and rock could not have come from the same location.

The laboratory cannot specifically determine where a sample of a questioned substance came from merely on the basis of known geological patterns. It may, however, provide you with knowledge of the exact contents of a sample. This information may provide clues to local areas that have the same general type of soil or rock indicated by the laboratory report.

MISCELLANEOUS LABORATORY EXAMINATIONS

In the laboratory, trace evidence is subject to a variety of examinations, some of which require the use of special equipment. The comments that follow are to familiarize you with the general nature of these examinations and with the instruments used. Such examinations normally are not conducted in the field; they are referred to the criminal investigation laboratory.

Ultraviolet Light

_{Ultraviolet light or} "black light" uses visible radiation of a slightly shorter wavelength than normal visible light. Ultraviolet light striking a surface is absorbed by some substances and, in turn, is radiated in a different colored light. In a darkened room, the rays are initially invisible but the effect on the substance is visible in that the light emission phenomenon resulting is one of fluorescence.

Numerous field uses may be made of ultraviolet light, and laboratory examinations may include the following:

1. Use of reflected ultraviolet light, or the fluorescence induced by it, often can quickly and easily indicate similarity or differences in a variety of substances. Stains on clothing that are not visible when viewed under ordinary light may become visible when viewed under ultraviolet. The grayish-white fluorescence of semen may be differentiated from the yellowish-green of urine.

2. Glass samples, similar in appearance and color under normal light, may be differentiated under ultraviolet. During the manufacturing process, trace materials may be introduced into the constituents purposely or accidentally, and the glass samples Can be differentiated by their fluorescent or reflective qualities.

3. Cosmetics, such as fingernail polishes, lipsticks, and rouge usually have distinguishing colors of fluorescence under ultraviolet light.

4. The paper and inks of documents usually show clearly their similarities or differences under ultraviolet light. Glues and other similar adhesives used to reseal envelopes usually can be distinguished by an examination under ultraviolet light.

Infrared Light

Infrared light is of a slightly longer wavelength than normal visible light. It has no fluorescent effect that can be seen by the unaided eye, but requires examination through infrared viewing equipment. Some materials that do not show a color under visible light do absorb and reflect infrared radiation, which can be detected photographically.

Laboratory applications include the following:

1. Differences shown by infrared light examination of paints and dyes often yield valuable investigative clues. Differences in opacity, transmittance, or reflectance usually are readily apparent.

2. Gunpowder residues on clothing may become visible even when obscured by dyes or stains such as bloodstains. A photograph of the powder residue pattern may permit proximity testing in the laboratory to determine the approximate distance that the muzzle of the firearm was held from the clothing at the time of firing.

3. Inks also maybe differentiated by examination under infrared illumination. Erasures on documents, as well as the writing or printing on charred documents, have been deciphered by using infrared light.

Spectrograph

Minute quantities of evidentiary material are often analyzed with the spectrograph, a laboratory instrument that produces a graph showing the basic constituents and trace elements of the substance examined

When a substance is burned, it sends out energy or light waves which are observed as colors. In the spectrograph, this light is passed through a prism and the resultant color pattern is focused on a photographic plate as a series of parallel lines of varying density. The different lines represent the different elements present, and their density or thickness corresponds to the quantity of the different elements present.

Analysis of this graphic portrayal will determine the nature of the substance and permit graphic comparison of two samples. Useful in analyzing primarily inorganic materials, the spectrograph is used in a criminal investigation laboratory for the examination of such things as paint, glass, dust, safe insulation, soil, wire, and other metals.

Spectrophotometers

Infrared and ultraviolet spectrophotometers permit qualitative and quantitative analysis of a substance through measurement of the substance's absorption of light rays of varying intensity. The laboratory application of this instrument lies primarily in identification and analysis of substances such as drugs, dyes, inks, plastics, oils, rubber, and stains, and in determining color and making color comparisons.

Gas-Liquid Chromatography

Both qualitative and quantitative analyses of a substance or mixture of several substances may be performed on a gas-liquid chromatography (GLC).

The material to be analyzed is injected into the GLC where it passes through a column that separates the components. As each component passes through a detector, the characteristic time to reach the detector and the relative amount of substance is recorded on a graph. Comparison of this graph with the graph of a known sample makes it possible to determine if two substances are of the same compositions.

This method is used primarily in comparison of paint fragments and accelerants found in arsons.