Micro evidence/Trace evidence is a broad term meaning any small piece of physical evidence that links a suspect to a crime scene. It’s mostly circumstantial class evidence, but depending upon the expertise and rules of admissibility, it can match individual characteristics. Fingerprints, toolmarks, and bitemarks (all forms of trace evidence), for example, use a points of comparison approach.
QDE and ballistics (also trace evidence areas) rely upon the “sufficiently certain” opinion of the expert. Other trace evidence fields (like toxicology, serology, and DNA) use probability estimates or odds-ratios. Microtrace evidence is a subtype of trace evidence involving minute, microscopic particles. The science of analyzing, identifying, and comparing microtrace evidence is called microanalysis.
It should be distinguished from the science of microscopy because the word micro in microanalysis refers to the size of the evidence, not the use of a microscope. Many other types of instrumentation are used by forensic microanalysts besides microscopes. Items traditionally examined include (and by no means are limited to): hair, fibers, paint, glass, dust, wood, soil, minerals, drugs, metals, perfumes, pollens, dyes, pigments, polymers, other materials, and atoms.
It’s not uncommon to see the name of the field shortened to hairs, fiber, paint, and glass. It’s difficult to gain a perspective on this field. It’s one of the areas where there’s the most confusion about the word “criminalist” which technically refers to laboratory personnel and “criminologist” which technically refers to an academic scientist.
To make matters worse, sometimes police crime scene technicians are referred to as “criminalists” when all they do is mainly “bag and tag” stuff that may contain microtrace evidence. In all fairness, however, police should be well-versed and better equipped in this area, and the phrase “crime scene analyst” is perhaps an improvement.
Forensic microanalysis relies upon instrumentation, which is contained in standards, operating procedures, test protocols, machine tolerances, owner manuals, dictionaries, etc., and written for industry and commercial (not law enforcement) applications. They’re fancy machine operators (sorry for the rather unflattering description), but they get to work with all kinds of microscopes, spectrographometers, chromographometers, and even nuclear reactors.