Lecture 17-18 Impression Evidence

1. Lecture 17-18Impression Evidence General & Scene Considerations

2. Using Technology

3. Finding Footwear Impressions2D Impressions Flashlight – Oblique Lighting Mirror Natural Light Infrared Ultraviolet Short & Long Wave RUVIS ALS

5. The Mirror Technique

6. Enhancing & Archiving Impressions

7. Composition of Dust and Soil • Dust – General Considerations: • General term for solid particles with diameters less than 500 micrometers • Comes from the atmosphere – sources include: • soil dust lifted up by wind, • pollution, • volcanic eruptions, • animals and • people.

8. House Dust • Human environment, e.g., • Homes, offices, etc., • Contain human skin cells, bacteria, plant pollen, human and animal hairs, feathers, textile fibers, paper fibers, minerals from outdoor soil, • Other materials, • All come from the local habitat. • The quantity and composition of house dust varies greatly with seasonal and environmental factors: • Surroundings, • exchange of outside air, • age of the house, • building materials and their condition • quantity of furniture and carpets, • state of preservation. • ventilation, • heating/cooling systems and • habits of those living in the house.

9. House Dust • House dust consists of inorganic (minerals) and organic matter, • Relative proportions vary considerably. • Dust from the homes with animals consists nearly completely of organic material. • In a study of 318 house samples, the proportion of organic matter ranged between <5% to >95%. • A survey of 11 homes showed • Organic content of house dust ranged between 25.7% to 56.5%, • Floor dust from seven offices had an organic fraction of 33%. • Variances vastly different in different regions – • North, south, east, midwest, southwest, west. • Rural or urban.

10. Enhancing 2D Impressions - Overview The Logic of Enhancing Impression Evidence • Understand the likely content of dust at scene • Archive – Photography • Determine type of Impression • Dry Residue Impressions • Electrostatic Lifter • Gel Lifter (Gellifter) • On paper • Chemistry (iron) • Wet Residue Impressions • Gel Lifter • Chemistry • Fe: Ammonium Thiocyanate • Fe/Mg: 8-hydroxyquinoline • Oils: Iodine/benzoflavone or starch • Dusting • Black magnetic dusting powder • Superglue fuming The current paradigm for enhancing dust impressions at crime scenes is single dimensional … typically involves lifting or chemical tests to visualize the mineral content of the dust. Sort of a crap shoot.

11. Electrostatic Lifting • Apparatus that creates static electricity between dust particles in the impression and a foil-backed Mylar film placed over the impression. If the print lifts, it is a dry residue print. That is, it was made from dust. Foil (silver) Side of Film (up) Electrodes Foil-backed Mylar Film Electrostatic Lifter Stun Gun Footprint in Dust Black Mylar Side on Dust Print: Foil Side Up. Electrode touching foil side + Ground Electrode Black Side of Mylar Film (down)

12. Arrows to Positive & Negative Electrodes Mylar Sheet Foil Side up The set up Fingerprint roller To Flatten Mylar Lifted Footwear Impression

13. Electrostatic Procedure • Place the metalized lifting film over the dust print. (dark side down) • Place the grounding plate about 8” next to the film. • Turn lifter so that the two metal probes on the back are resting on the grounding plate and the single probe is resting on the film. • Turn on the device and the film will be sucked down onto the print. • Gently brush over the film to remove any air bubbles. • Lift and you have your dust print.

14. Effects of Humidity and Temperature • The issue of humidity studied by investigators employing a similar technique ESDA for the detection of indented writing. • Studies show >>> humidity necessary … becomes detrimental when the relative humidity goes above 98% at room temperature … quality drops off. • At cold temperatures, even lower humidity causes a decrease in the quality of the highlighted indented printing. • ESDA is not an electrostatic lifter, but the principle is the same, and one might expect similar deterioration of the quality of prints using an electrostatic lifter. • Generally, normal use of electrostatic lifter under normal conditions of temperature and humidity should provide reliable results. • HOWEVER … absence of humidity … ESDA process requires humidity … opens the possibility that the absence or near absence of humidity may also affect the quality of electrostatic lifts.

15. Electrostatic detection apparatus (ESDA) • ESDA stands for Electrostatic Detection Apparatus. Used to produce a permanent 'lift' from paper which provides a visual map of indented impressions • Non-destructive. The paper under examination remains in exactly the same state, still available for other examinations. • Extremely sensitive - indentations found up to seven sheets below the page where the original writing was made. • ESDA works by stretching a Mylar film (like Clingfilm) over the document being examined. • Mylar film is electrostaticaly charged. • Where the paper is smooth, charging is generally uniform, however where the fibers of the paper have been disturbed by paper-paper contact caused by indentations, the electrostatic charge is different versus the background. • Creates latent image. In order to visualize this latent image, Black toner similar to that used in laser printers is applied to the surface of the Mylar. • Toner preferentially sticks where the electrostatic charge congregates • Areas of the indentations … an image with a grey toner background and darker toner traces in the areas where there are indented impressions. • Image is made permanent as a 'lift' by placing clear 'sticky backed plastic' over • Variables: Type of paper, the type of pen or stylus used, the number of sheets of paper between the writing and the sheet holding the impressions, the humidity at the time the impressions were made, the humidity at the time the ESDA lift was made, the method by which the toner is put onto the Mylar film*, and the amount and direction of the electrostatic charge put onto the Mylar film. • Not suitable for the examination of loose fibred paper such as newspaper or very glossy paper such as magazine covers. • Liquid will completely destroy the ESDA impression. … fingerprint treatment should be done AFTER any ESDA examination. • Toner can be put onto the Mylar film using three methods: cascading tiny glass beads coated with toner over the surface, puffing an aerosol of toner powder over the surface or using a device similar to a powder puff to apply the toner.

16. Storing Electrostatic lifts • Electrostatic lifts - fragile and must be protected. • Storing in flat boxes preserves better than other methods: • Do not roll in tubes. • A problem with flat storage is that dust is attracted to surface because the lift retains a residual static charge – it stops the dust from falling off the Mylar film. • Problem exacerbated when lifts exposed to open air or in low-grade cardboard. • Even lifts stored in a high quality cardboard will lose residual charge over time resulting in the complete loss of the impression. • Storage conditions: • High humidity increases rate of residual charge degradation • Store with a desiccant (silica gel) taped to inside of box. • Recommended to store the lifts so that the humidity does not exceed 50%.

17. If the print does not lift, it is a wet residue print. • Advantage of electrostatic lifting is preservation of the impression detail onto a black, Mylar surface. • What if, however, the impression does not lift? Is that proof that the impression was formed from a wet shoe? Differentiating Dry& Wet Residue 2D Impressions Impression at Scene Photograph Electrostatic Lift Successful Unsuccessful Dry Residue Impression Wet Residue Impression Photograph Enhance Preserve Impression Magnetic Powder Powder Suspension Chemical Enhancement Protect in Lift Box Protect with Gel Lifter Photograph

18. Gelatin Lifters (gellifters) For preservation purposes, they serve a similar function as electrostatic lifters • Effective multi-tasking tools. • Commercially available in two forms: • Rubber-backed gelatin-based in black, white or • Clear gelatin on a clear backing. • Semi-sticky surface lifts dry residue impressions AND wet residue impression. • Not reliable for differentiating between dry and wet residue impressions. • Do not require static charge. • “Sticky” surface “grabs” dust impression and sticks it to the surface of lifter. • Also pick up any surrounding, contaminating material such as dust, which can mask the lifted impression. Black Gellifter Lifting Footwear Impression

19. Gelatin Lifters (gellifters) • For dry residue prints, the light tan color of the impression is nicely off-set by the black of the gellifter. • Like electrostatic lifters, gellifters can lift impressions from hard surfaces, paper, carpeting, clothing, etc. • They are particularly useful on vertical surfaces. • Storage: • In uncovered high quality cardboard boxes works well. • Generally recommended that low grade cardboard boxes not be used because … tend to shed fibers onto the lifted image. • Also, breathable boxes will keep condensation from forming on the lifts. • Remove acetate sheet that comes with the lifter • Removing it later can remove some of the image. • Store the lifts in the same way as electrostatic lifts: high grade cardboard box without the acetate cover. • Over dusted or dense dust impressions can benefit from repeated removal of the acetate cover because this tends to remove some of the excess dust and render the lifted impression sharper.

20. Adapted from the BVDA gellifter brochure: http://www.bvda.com/EN/download/Gellifter_brochure.pdf,