Preface by Richard E. Bisbing, McCrone Associates, Inc.

In the Locard tradition, forensic scientists most often use microscopic trace evidence as a means to connect victims and suspects with each other or the scene of the crime.  The principal means to make that association is by direct comparison of microtraces on their clothing or objects at the crime scene with possible sources.  For example, foreign fibers found on the victim’s clothing are compared directly with fibers comprising the suspect’s clothing, or paint chips on a screw driver are compared directly with paint from the window sill.

In a few cases, sourcing is attempted before suspects are identified and comparison samples obtained, most commonly in hit and run accidents where paint from the run-away vehicle remains at the scene of the accident.  The paint is analyzed and compared with databases, often allowing the laboratory to predict the make, model and year of manufacture of the run-away vehicle.  There have also been notable cases where carpet fibers were found on the victim’s clothing and, through cooperation with major car manufacturers, the carpet fibers were identified and determined to have been installed in a single model over just a couple of years.  A model case using leaf litter appeared recently in the Journal of Forensic Sciences as a Letter to the Editor (Volume 48, Number 3, May 2003, page 696) [http://journalsip.astm.org/jofs/].  Although, sometimes painstakingly difficult and time consuming, these cases illustrate the potential value of microscopical geo-sourcing.

John Delly began a short series on the principles and practices of microscopical geo-sourcing, starting with minerals, in the last quarter and continues with combustion products here.  We again invite our readers to contribute articles about other materials that can likewise be geo-sourced, such as pollen, seeds, sand, etc.  As usual, we encourage the contributions to be accompanied with color images.  We are not interested in news and views on the other geo-sourcing, that is, outsourcing IT services to some other part of the world.  On the other hand, we would be interested in such projects as "Geo-Sourcing of Controlled Substances by High Field Deuterium NMR Spectroscopy and Stable Isotope Ratio Mass Spectrometry, " or “Geo-Sourcing of Cocaine Using Isotopic Ratio Mass Spectrometry (IRMS) and Trace Alkaloid Analysis” as a means for the U.S. Drug Enforcement Administration to determine the geographical origin of controlled substances, (http://www.emsl.pnl.gov/new/highlights/030100.shtml; http://www.carleton.ca/~bhollebo/Chem2303/AlkaloidAnalysis.htm)

Part 2 – Combustion Products

Combustion product particulates are microscopic dust particles that bear characteristic indicators that the original parent, or host, material was exposed to and/or altered by heat.  The exposure to heat may be mild or extreme, and the host material may be almost anything.  Many examples come to mind, such as the deliberate burning of coal or petroleum or gas or wood, or a combination of these, for the purpose of producing heat for personal comfort or survival in cold climates, and for cooking, or for a variety of industrial processes, including power generation.  The burning may be accidental, as in forest and grass fires, or it may be the deliberate result of arson.

Most of us think of combustion resulting in char and ash, leaving no evidence of the original material behind.  Actually, nothing could be farther from the truth.  Combustion product particulates can provide valuable information about the original material and its origin.  Physical and chemical changes that take place during the combustion process are numerous, but let us look at a typical, common example by way of illustration, the burning of coal.