An Introduction to Household Dust
Written by Nicholas Petraco & Nicholas D. K. Petraco   

THE AUTHORS' HYPOTHESIS, “that the combination of animal, mineral, vegetable, and synthetic materials within any given household dust specimen, in combination with the DNA of its living inhabitants and visiting individuals, offers to the forensic scientist a formidable cocktail of irrefutable, scientifically sound data which is unique to any single location, and thus can be used to unequivocally identify any site on this planet,” is the underpinning for their work. The authors offer this chapter toward proving their thesis.

This article appeared in the September-October 2020 issue of Evidence Technology Magazine.
You can view that full issue here.

This article is an excerpt from “A Guide to the Analysis of Forensic Household Dust Specimens and Their Statistical Significance,” a chapter in Forensic Science Handbook, Volume 1 (Third Edition)

Introduction
The need for the increased utilization of trace evidence in the crime laboratory has been pointed out.1,2 McCrone has estimated that considerably less than 1% of all the potential trace evidence in crimes is ever examined.3 This phenomenon is peculiar indeed, considering the fact that trace evidence has been shown time and again to be the most valuable source of investigative information and proof. These data can be used to: (1) help solve crimes; (2) associate the people, places, and things involved in the crime; (3) deduce the occupation(s) of the principal(s) involved in the crime; and (4) reconstruct the crime scene and/or the event itself.4–22

A century ago, Hans Gross speculated that dust is a representation of our environment in miniature. Gross further proposed that by recognizing the constituents composing a particular dust sample one could estimate the surroundings from which the dust originated, and that this information could be used to help solve crimes.4 This fact left the scientific investigator with a difficult challenge: the need to develop analytical methods that could be used to identify minute traces of the many different types of materials that occur in dust as trace evidence. McCrone, Delly, and Palenik’s work with Aroclor®, polarized light microscopy, and The Particle Atlas series has certainly established an effective methodology for accomplishing the identification and characterization of all types of dust specimens.23 Following their lead, some forensic scientists have developed schemes utilizing different mounting media for identifying some of the substances that occur as trace evidence. Graves published an excellent article on the characterization of the minerals in soil, in which he utilized a Cargille® oil having refractive index of 1.54.24 Fong was first to publish a scheme for the identification of different synthetic fibers in a single mounting medium having a refractive index of l.525.25 Next, Petraco described a rapid screening method for identifying synthetic fibers in dust and a microscopic method for animal hair identification in Melt Mount® 1.539.26 Many of the theoretical principles and methods necessary for the collection, identification, examination, comparison, and evaluation of the various types of trace materials that occur in dust have already been presented in Volumes I and II of this Handbook series.27–34 The primary goal of this chapter is to present a microscopical guide for the identification and characterization of the components of dust specimens mounted in a single refractive index medium, namely Melt Mount 1.539. It is intended that the chapter will provide the forensic microscopist with a reference that will serve as an introductory guide to the examination of the trace materials commonly encountered in household dust specimens:

  1. Human skin cells
  2. Human hair
  3. Animal hair
  4. Synthetic fibers
  5. Mineral and glass fibers and particles, plaster chips, concrete particles, paint chips, glass and mineral fragments, and other related materials
  6. Miscellaneous substances: white and blue cotton fibers, food stuff particles, plant hairs, pollens, vegetable fibers, paper fibers and plant matter, starch grains, feathers, and glitter
  7. Construction materials and so on

Many of the less traditional forms of trace evidential materials found in dust specimens have already been discussed by Palenik in the second edition of Volume II32 and thus will not be covered in this chapter. However, serious readers should familiarize themselves with the identification of these substances because they will no doubt be encountered in their casework.

It is the authors’ hope that this work will help guide the novice and experienced forensic examiner through the successful analysis of household dust specimens, such as the one depicted in Figure 1. It is also the authors’ wish that this effort will help foster the utilization of polarized light microscopy and trace evidence in the crime laboratory.



Figure 1. Specimen of questioned dust from a double homicide investigation. The specimen is mounted in Melt Mount 1.569 and contains the following trace materials: human hairs; animal hairs; synthetic fibers; vegetable fibers; blood flakes; insect parts; features; food particles; glass fragments; and mineral fragments.

The formation of household dust is a complex phenomenon. The authors’ research indicates that a hair, fiber, feather, or piece of fibrous material initiates the process. Forces such as convection currents, static electricity, breezes, drafts, and Brownian motion, all together, over time, cause additional lengths of fibrous materials to coalesce into a cagelike structure which trap and hold fragments of particulate matter, that is, skin fragments, plant matter, mineral grains, and food particles as demonstrated in Figure 2.


Figure 2. Formation of household dust (dust bunnies).

Whereas dust traces can encompass an infinite number of different materials, the authors have found that three primary morphological forms compose most specimens of dust:

  1. Fibrous materials
  2. Particulate matter
  3. Structured substances

The three primary morphological forms of materials commonly observed in household dust specimens are listed in Table 1.

When searching for dust specimens, one must realize that there is no limit to the places or things specimens of dust can be found in or on. Therefore, one must keep an open mind when searching for dust. Some of the more common places and items to examine for dust traces are: under furniture, under radiators, attached to fans, in room corners, on items of the suspect’s clothing such as shoes, outer garments, etc. As well as the victim’s or suspect’s clothing or vehicle, any weapons or objects used to commit the crime, and so forth. It should be noted that the type of crime can often guide the examiner’s collection efforts. Gaudette presents a comprehensive listing for fibers.34 Many of his suggestions apply to the other elements found in dust, and for aggregate dust specimens as well.

Of paramount importance to the successful analysis of forensic dust specimens is the procedure employed in the collection and preservation of the various items of physical evidence to be examined. The associations made possible by dust traces are based primarily on the mutual exchange principle attributed to Dr. Edmond Locard by Nickolls.35 If one is familiar with Locard’s original work, one can see that all the basic elements of this hypothesis are clearly set forth.36 Simply paraphrased, this principle postulates “that whenever two people, places, and or things interact there is always a mutual cross transfer of trace materials from one to the other.”

The trace materials that are transferred during these contacts make the stated associations and deductions possible. Therefore, accidental contact between the items of physical evidence that are to be processed for trace evidential materials must be guarded against to prevent contamination. To eliminate this possibility, one must keep each item of physical evidence separate. This is easily accomplished by wrapping each item individually in paper, securing them with a druggist fold, or by placing each in a separate paper container. Prior to wrapping, the items should not be handled or allowed to come into contact with common surfaces. Vacuum sweepings or tape lifts should also be packaged in separate paper containers. It is the authors’ opinion that plastic containers should be avoided because they often possess an electrostatic charge that can attract foreign dust traces—causing contamination of the evidence—or repel potentially valuable dust traces. Another factor that is extremely important is whether the item(s) of physical evidence is wet or dry. If wet, the item(s) should be air dried prior to packaging. If dry, the item(s) can be packaged in paper as previously described. Here again, plastic containers should be avoided because they retain moisture, thereby encouraging microbial (bacterial or fungal) growth that may cause biological decomposition. Finally, one must keep in mind that dust traces, due to their nature, are easily lost. To prevent inadvertent loss, the paper packaging should be free of small holes or perforations.

Once received at the laboratory, the dust traces must be collected from each item of physical evidence. A comprehensive discussion of the collection procedures for the recovery of dust has been given in this Handbook series.37 Therefore, this section covers only the methodology normally used by the authors. It has been the authors’ combined experience that a systematic approach is vital when retrieving dust traces, and that each item of physical evidence should be processed separately utilizing the following procedure.

The item to be examined should be removed from its container and laid out on a clean piece of paper that has been placed atop a well-illuminated examination table. The size of the paper is dictated by the size of the article being processed. Ideally, the room in which the examination takes place should be dust free (a clean room). If this is not possible, the room should be kept as clean as possible, and be situated in a low-traffic area of the laboratory. Adequate table-top space for laying out the items of physical evidence should be available. Each item of physical evidence is first observed visually, and then with a stereomicroscope. As pointed out by Palenik,37 a boom stand is most useful for this purpose. In addition, a floor-type surgical operating microscope with a magnification range of 2x to 25x is an excellent device for scanning large objects for traces of dust. Various forms and techniques of illumination (oblique lighting, monochromatic laser light, ultraviolet light, xenon or quartz halogen lamps with fiber optics or gel cables, and so forth) can aid in the visual location of dust traces. After location and documentation (sketching, photographing), all visible traces can be removed by hand with forceps or a needle.

Next, the item of physical evidence should be processed with some sort of transparent tape, as first suggested by Frei-Sulzer.38 When using tape lifts to collect dust traces, the examiner should be aware that the position of the trace evidence on the item of physical evidence can be crucial to any reconstruction efforts. Therefore, it is imperative to document the area(s) from which these traces are collected. Several studies and methods employing different approaches and adhesive materials have been published;13,16,38–42 each has its own merits. The adhesive material and method to be used should be decided on by the individual examiner, depending on his or her own needs and resources. The authors use 1-inch-wide transparent latent fingerprint lifting tape. The item to be processed is taped in segments or quadrants. For example, a pair of men’s pants would be taped as follows: (1) the upper or lower (U/L) front right leg, (2) the U/L front left leg, (3) the front top portion, (4) the U/L rear right leg, (5) the U/L rear left leg, and (6) the rear top portion; inside areas such as pockets, cuffs, and interior legs are processed when necessary. Each tape lifting is marked for identification as to item and segment taped. The tape lifting is placed adhesive side down onto a clear Mylar® sheet to prevent contamination. After the taping process has been completed, the underlying paper should be checked for any trace material that may have fallen from the item being examined. This material should be collected and preserved for examination. The tape liftings are observed with a stereomicroscope to locate traces of dust. Contrasting color backgrounds made from pieces of oak tag are useful when screening tapes. All tape liftings should be stored in paper envelopes.


Figure 3. Trace evidence vacuum trap as described by Dr. Paul Kirk.

Finally, when necessary, the item can be vacuumed for dust traces. The vacuum sweepings trap described by Kirk can be used as demonstrated in Figure 3.43 Additionally, another effective trace evidence vacuum trap has recently been described as well.44 These devices are useful because they aid in the preliminary collection of the trace materials often found in sweepings. It should be pointed out that, although very efficient, vacuuming has many disadvantages; the primary one being that vacuuming often comingles the materials which were recently deposited (often the most important) with substances which were deposited long ago. In any case, vacuum sweepings should be used only when absolutely necessary, only after visual and taping procedures have been previously conducted.19,44,45

Once collected, the household dust specimens are best preserved by storing in paper containers (boxes or paper folds), screw top glass jars, and heavy-duty antistatic plastic jars, until examination, or for future reference.


References

  1. W. C. McCrone, “Particle Analysis in the Crime Laboratory,” in The Particle Atlas, Vol. 5, W. C. McCrone, J. G. Delly, and S. J. Palenik, eds. (Ann Arbor, MI.: Ann Arbor Science Publishers, 1979), pp. 1379–401.
  2. N. Petraco, “The Occurrence of Trace Evidence in One Examiner’s Casework,” J. Forensic Sci., 30, 1985, 485–93.
  3. W. C. McCrone, “Particle Analysis in the Crime Laboratory,” in The Particle Atlas, Vol. 5, W. C. McCrone, J. G. Delly, and S. J. Palenik, eds. (Ann Arbor, MI.: Ann Arbor Science Publishers, 1979), p. 1379.
  4. H. Gross, Criminal Investigation adapted from System Der Kriminalistik, by J.C. Adams, (London, England: Sweet and Maxwell Limited, 1924), pp. 144–47.
  5. A. Schneider, “Police Microscopy,” J. Criminal Law Criminol. Police Sci., 11, 1920, 217–21.
  6. E. Locard, “The Analysis of Dust Traces,” Am. J. Police Sci., I, 1930, Part I 276–98, Part II 401–18, Part III 496–514.
  7. H. T. F. Rhodes, Clues and Crime, (London: John Murray, 1933), pp. 33–5.
  8. H. S.derman, and J. J. O’Connell, Modern Criminal Investigation, (New York and London: Funk and Wagnalls, 1935), pp. 243–50.
  9. A. Lucas, Forensic Chemistry and Scientific Criminal Investigation, (New York: Longmans, Green & Co.; London, Edward Arnold & Co. Publishers Limited, 1935), p. 64; pp. 152–60.
  10. C. H. O’Hara, and J. W. Osterburg, An Introduction to Criminalistics, (New York: The MacMillan Co., 1949), pp. 30–6.
  11. P. L. Kirk, Crime Investigation, (New York: Interscience Publishers, 1953), pp. 3–11.
  12. L. C. Nickolls, “The Identification of Stains of Nonbiological Origin,” in Methods of Forensic Science, Vol. I, F. Lundquist, ed. (New York: Interscience Publishers, 1962), pp. 335–71.
  13. M. Frei-Sulzer, “Coloured Fibres in Criminal Investigations with Special Reference to Natural Fibers,” in Methods of Forensic Science, Vol. 4, A. S. Curry, ed. (New York, NY: Interscience, 1965), pp. 141–75.
  14. S. J. Palenik, “The Determination of Geographical Origin of Dust Samples,” in The Particle Atlas, Vol. 5, W. C. McCrone, J. G. Delly, and S. J. Palenik, eds. (Ann Arbor, MI: Ann Arbor Science Publishers, 1979), pp. 1347–61.
  15. N. Petraco, “A Guide to the Rapid Screening, Identification, and Comparison of Synthetic Fibers in Dust Samples,” J. Forensic Sci., 32(3), 1987, 768–77.
  16. M. C. Grieve, “The Role of Fibers in Forensic Science Examinations,” J. Forensic Sci., JFSCA, 28(4), 1983, 877–87.
  17. H.A. Deadman, “Fiber Evidence and The Wayne Williams Trial,” FBI Law Enforcement Bulletin, March 1984, pp. 13–20 & May 1984, pp. 10–9.
  18. R. Saferstein, Criminalistics, 3rd edition, (Englewood Cliffs, NJ: Prentice-Hall Inc., 1987), pp. 183–220.
  19. P. R. De Forest, R. E. Gaensslen, and H. C. Lee, Forensic Science an Introduction to Criminalistics, (New York: McGraw-Hill, 1983), pp. 146–67.
  20. B. D. Gaudette, “Fibre Evidence,” R.C.M.P. Gazette, 47(12), 1985, 18–20.
  21. R. Saferstein, ed. Forensic Science Handbook, Vol. I, Vol. II, (Englewood Cliffs, NJ: Prentice-Hall Inc., 1982, 1988).
  22. N. Petraco, “Trace Evidence—The Invisible Witness,” J. Forensic Sci., 31, 1986, 321–28.
  23. W. C. Mc Crone, and. G. Delly, eds. The Particle Atlas, 2nd edition, (Ann Arbor, MI: Ann Arbor Science Publishers). vol. I 1973, vol. 2 1973, vol. 4 1973, and W. C. McCrone, J. G. Delly, and S. J. Palenik, eds., vol. 5 1979.
  24. W. J. Graves, “A Mineralogical Soil Classification Technique for the Forensic Scientist,” J. Forensic Sci., 24, 1979, 323–38.
  25. W. Fong, “Rapid Microscopic Identification of Synthetic Fibers in a Single Liquid Mount,” J. Forensic Sci., 27, 1982, 257–63.
  26. N. Petraco, “A Microscopical Method to Aid in the Identification of Animal Hair,” The Microscope, 35, 1987, 83–92.
  27. P. R. De Forest, “Foundation of Forensic Microscopy,” in Forensic Science Handbook, R. Saferstein, ed. (Englewood Cliffs, NJ: Prentice-Hall Inc., 1982), pp. 416–528.
  28. R. E. Bisbing, “The Forensic Identification and Association of Human Hair,” in Forensic Science Handbook, R. Saferstein, ed. (Englewood Cliffs, NJ: Prentice-Hall Inc., 1982), pp. 184–221.
  29. E. T. Miller, “Forensic Glass Comparisons,” in Forensic Science Handbook, R. Saferstein, ed. (Englewood Cliffs, NJ: Prentice-Hall Inc., 1982), pp. 139–83.
  30. J. I. Thornton, “Forensic Paint Examination,” in Forensic Science Handbook, R. Saferstein, ed. (Englewood Cliffs, NJ: Prentice-Hall Inc., 1982), pp. 529–71.
  31. R. C. Murray, “Forensic Examination of Soil,” in Forensic Science Handbook, R. Saferstein, ed. (Englewood Cliffs, NJ: Prentice-Hall, 1982), pp. 653–71.
  32. S. Palenik, “Microscopy and Microchemistry of Physical Evidence,” in Forensic Science Handbook, vol. II, R. Saferstein, ed. (Englewood Cliffs, NJ: Prentice-Hall, 1988), pp. 161–208.
  33. B. D. Gaudette, “The Forensic Aspects of Textile Fiber Examination,” in Forensic Science Handbook, vol. II, R. Saferstein, ed. (Englewood Cliffs, NJ: Prentice-Hall, 1988), pp. 209–72.
  34. Ibid., pp. 214–15.
  35. L. C. Nickolls, “The Identification of Stains of Nonbiological Origin,” in Methods of Forensic Science, Vol. 1, F. Lundquist, ed. (New York: Interscience Publishers, 1962), pp. 335–37.
  36. E. Locard, “L’analyse des poussieres en criminalistique,” Revue Internationale de Criminalistique, 1 Juillet 1929, pp. 176–249.
  37. S. J. Palenik, “Microscopy and Microchemistry of Physical Evidence,” in Forensic Science Handbook, vol. I, R. Saferstein, ed. (Englewood Cliffs, NJ: Prentice Hall, 1988), pp. 164–68.
  38. M. Frei-Sulzer, “Preserving Micro-Traces Under Adhesive Bands,” Kriminalistik, 19(20), 1951, 190–94.
  39. E. Martin, “The Behavior of Textile Fibres in Contact with the Glue of Adhesive Transparent Strips Used for Collecting Specimens,” Int. Crim. Police Rev., 188, 1965, 135–41.
  40. M. C. Grieve, and E. F. Garger, “An Improved Method for Rapid and Accurate Scanning of Fibers on Tape,” J. Forensic Sci., 26, 1981, 560–63.
  41. M. Y. Choudhry, “A Novel Technique for the Collection and Recovery of Foreign Fibers in Forensic Science Casework,” J. Forensic Sci., 33, 1988, 249–53.
  42. T. M. Hopen, “Dust Collection Method,” Microscope, 48(4), 2000, 213.
  43. J. R. Millette, and P. Few, “Sample Collection Procedures for Microscopical Examination of Particulate Surface Contaminants,” Microscope, 49(1), 2001, 21–7.
  44. N. Petraco, “The Occurrence of Trace Evidence in One Examiner’s Casework,” J. Forensic Sci., 30, 1985, 486.
  45. S. Palenik, “Microscopy and Microchemistry of Physical Evidence,” in Forensic Science Handbook, vol. II, R. Saferstein, ed. (Englewood Cliffs, NJ: Prentice-Hall, 1988), pp. 165–67.
 
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