FBI Soil Examination Unit
Definition
The specialist unit at the FBI Laboratory in Quantico, Virginia, that has conducted forensic soil comparisons in federal criminal cases since the late 1960s and maintains a national reference soil database.
- Location
- FBI Laboratory, Quantico, Virginia
- Active since
- Late 1960s
- Function
- Forensic soil comparison in federal cases
- Resource
- National reference soil database
Common questions
What makes soil comparison a specialist function rather than something any trace examiner can do?+
Soil composition varies with mineralogy, organic content, particle size distribution and regional geology, so reliable comparison requires geological and pedological expertise alongside standard microscopy and chemical analysis, which is why the FBI maintains it as a dedicated unit rather than folding it into general trace evidence.
How does a national reference database help in an individual soil comparison case?+
It lets examiners situate a questioned soil sample's characteristics against known regional and local soil profiles, helping establish whether a sample is consistent with, or inconsistent with, a specific location rather than relying solely on side-by-side comparison to a single known sample.
Related terms
- Bayesian Inference
- A framework for updating probability estimates in the light of new evidence; in forensic science, used to combine the prior probability of...
- Control Sample
- A water sample collected from the suspected drowning environment at or shortly after the time of body recovery. Its diatom assemblage is...
- ENFSI ENG-FG1
- The European Network of Forensic Science Institutes' guidelines for forensic geological evidence, published in 2018 by the Expert Working Group on Forensic...
- Likelihood Ratio (LR)
- The ratio of two conditional probabilities: the probability of the observed evidence given the prosecution's hypothesis (same source), divided by the probability...
- Mahalanobis Distance
- A multivariate distance measure that expresses the separation between two observations in units of the population standard deviation, accounting for covariance; used...
- Murray-Tedrow Framework
- The tiered forensic-soil comparison protocol established by Raymond Murray and John Tedrow in their 1992 text 'Forensic Geology,' which organises soil examination...
- Principal Component Analysis (PCA)
- A multivariate statistical method used in fire debris research to reduce chromatographic data matrices to principal components that capture major variance. Used...
- Prosecution Proposition
- In the Bayesian evidence framework, the proposition that the questioned evidence item was in contact with or came from the crime scene;...
- Transfer and Persistence
- The processes by which soil particles move from a source to an evidence item and remain there; relevant to forensic comparison design...
- Verbal LR Scale
- A standardised conversion table from numerical likelihood ratio values to phrases such as 'moderate support' or 'very strong support' for one of...
- Within-Scene Variability
- The natural compositional variation of soil properties over short distances within a single scene; must be characterised by multiple control samples before...