Particle Combination Analysis (PCA)
Particle Combination Analysis or PCA is a relatively new approach that uses co-occurring particles to establish and test associations between people, places, and objects.PCA exploits the particles in dusts, which are ubiquitous and in infinitely varying combination, to answer questions such as:
- Where did this object or person come from
- What activities are going on near the place where an item or person was
- Was this item in a specific person’s possession
- Can a person or an item be linked to another specific item or place
Very Small Particles (VSP) are fine dust particles adhering to virtually any object. VSP are everywhere – dusts, pollen, scents, vapors, molecules. There are literally thousands of particles on everyone and everything. Hundreds of these particles would fit on a cross section of a human hair.
VSP are the result of the object’s unique history of exposure, from people who are nearby, and from each location passed through. They adhere to clothes and objects creating a mix of particles with almost infinite variation.
The large numbers of particles and their infinite combination can provide a particle profile signature with the potential to convey whether someone or something has been near a specific person, object, place, or activity.
Examples of the variety of particles routinely and easily recovered from items:
The large numbers and varieties of these particles yield signature profiles…
which in turn provide verifiable links to the profiles of places, people, or other items:
A New Forensic Method
Particle Combination Analysis or PCA is fundamentally different from traditional trace evidence used in police work that most people are familiar with. In fact, other than that both involve things smaller than people usually examine with a naked eye, they have little in common. There are three differences in particular:
Size – VSP are much smaller particles. Dozens or more would fit on a cross section of traditional trace evidence items such as hairs or fibers.
Number and Variation – Not only are there hundreds or thousands on virtually any object of interest, there are hundreds or thousands of different types of particles. This means there are hundreds of times as many to be found and, they are much more likely to occur on any piece of evidence.
Process for making inferences – Unlike traditional trace evidence analysis which involves a process of searching for matches with single particle types, PCA involves making inferences from combination of particles. These combination can either be matched with known sets of combination, or inferences can be made from the character and make-up of the combination itself. The strengths of associations resulting from these comparisons can be measured quantitatively and objectively, reducing observer bias while preserving evidential value.
PCA can be applied to a range of investigative needs
Not my Gun, Not my Drugs – Investigations or prosecutions involving physical evidence such as guns, drugs, or stolen property.Comparison of
- PCA Profiles from evidence, with
- PCA Profiles from a suspect’s pocket, closet, backpack, car, residence
Can provide a very strong link or show very unlikely association.
Investigating a series of crimes – drug seizures, weapons, explosives, human traffickingComparison of
- PCA Profiles from evidence, suspects, or location of an individual crime, with
- PCA Profiles from evidence, suspects, or locations from similar crimes
Can provide links that illuminate criminal organizations, gang activity, and distribution networks.
Significantly, the profiles can come from different sources or types of evidence.
Comparison of
- PCA Profiles from packaging, materials and assembled components, with
- PCA Profiles from a database for created for specific countries
Can provide rapidly verify or refute the labeled origins.
Shoes – Was this person walking at the crime scene? PCA profiles on shoes can be separated into those recently or previously acquired. These provide information about recent and past places walked.Comparison of
- PCA Profiles from shoes
- PCA Profiles from the location of a crime
Can provide a very strong link or show that it is very unlikely that the shoes were worn at the crime scene.
Where’s the building?PCA profiles, together with in-depth analysis of the component particles have been used to narrow the search for locations where drugs were made, bombs were assembled, or a person’s clothing came from. The progress and approach are often stepwise
- From somewhere in a country to a specific region
- From a region to a specific neighborhood
- From a neighborhood to a specific building
The results come with details about the nearby environment that are used to screen locations – such as nearby trees and shrubs, water, open spaces, and commercial activity.
The approach can be applied to evidence or to shipped materials such as explosives, drugs, and counterfeit or controlled products.
It can also be used for finding the originating farm, processing facility, or factory that is the source of pollution, disease, or contaminated food.
Whether PCA Profiles be obtained from the edges of tape from evidence or crime scenes, and
Whether these profiles be used to determine associations with PCA Profiles obtained from edges of a roll found in a search of a suspect’s vehicle or residence
Details and Additional Information
Examples and details of contributions to previous investigations are available
We are happy to provide information and assistance to law enforcement and some types of commercial investigative
Stoney Forensic PCA Research
Our most recent PCA research has been funded through multiple awards from the National Institute of Justice:
Analysis of Small Particles Adhering to the Edges of Duct Tape as a Means to Make Associations in a Way that is Independent of Manufactured Characteristics 2021-2022
Determination of Key Factors in Particle Combination Analysis to Enable Systematic Improvement, Optimization and Transition to Practice 2018-2019
Evidential Value of Particle Combination Profiles On Common Items of Physical Evidence 2016
Differential Sampling of Footwear and Quantitative Particle Analysis to Separate Relevant Evidentiary Particles from Background Noise 2015-2017
Exploitation of Very Small Particles to Enhance the Probative Value of Carpet Fibers 2013-2014
Prior research efforts into methods and applications of PCA and VSP were funded by various government and private organizations for a range of purposes. These projects spanned over 10 years and produced both original research and new methods to address specific investigative efforts. Details of these efforts and their results are available.
Stoney Forensic PCA Articles and Talks
David Stoney has been a leading academic, researcher, instructor, and journal editor in areas relating to analysis and interpretation of microscopic particles for over 30 years. Stoney Forensic, Inc has been at the forefront of developing practical applications and programmatic applications for over 20 years. Results of these efforts include more than 100 published papers and invited talks at professional meetings. A few important ones are listed here.
Analysis of Small Particles Adhering to the Edges of Duct Tape as a Means to Make Associations in a Way that is Independent of Manufacturing Characteristics
NIJ Research Symposium 2022
‘Identification of Key Factors for SEM/EDS Analysis of Particles’ FSI 2021
Key Factors in Particle Combination Analysis to Enable Systematic Improvement, Optimization and Transition to Practice – AAFS 2-22-18
‘Discrimination and Classification among Common Items of Evidence using Particle Combination Profiles’ – Forensic Science International, Vol 289, pp. 92-107, 2018.
‘Utilization of Environmentally Acquired Very Small Particles as a Means of Association’ – Article by Dr. David Stoney et al. – Forensic Science International. Vol. 254, 26-50, 2015.
‘Particle Combination Analysis: Developing a New Approach to Forensic Trace Evidence’ Talk by Dr. David Stoney – National Institute of Justice 2015 Research Grantees Meeting, Orlando, FL, February 17, 2015.
‘Computational Methods Supporting Particle Combination Analysis: Application to Very Small Particles on the Surface of Carpet Fibers’ Talk by Dr, David Stoney – Proceedings of the American Academy of Forensic Sciences, Vol. 20, pp. 85-86, 2014.
‘Illustration and Analysis of a Coordinated Approach to an Effective Forensic Trace Evidence Capability’ – Article by David and Paul Stoney – Forensic Science International, Vol. 253, pp. 14-27, 2015.
‘Exploitation of Very Small Particles to Enhance the Probative Value of Carpet Fibers’ – Article by Dr. David Stoney et al. – Forensic Science International, Vol. 252, pp. 52-68, 2015.
‘A Critical Review of Forensic Trace Evidence Analysis and the Need for a New Approach’ – Article by David and Paul Stoney – Forensic Science International, Vol. 251, pp. 159-170, 2015.
‘Inferential Source Attribution from Dust: Review and Analysis’ – Article by Dr. David Stoney et al. – Forensic Sci Rev, Vol 25, pp.107-142, 2013.
‘Particle Combination Analysis for Predictive Source Attribution: Tracing a Shipment of Contraband Ivory’ – Article by Dr. David Stoney et al. -, Journal of the Association of Trace Evidence Examiners, Vol. 2, No. 1, pp. 13-72, December, 2011.
‘Time to Rethink Dusts’ – Talk by Dr. David Stoney at 2011 NIJ/FBI Trace Evidence Symposium.