Forensic Science: Trace Evidence

Small quantities of material transferred, deposited, or recovered during an event that may assist in reconstructing contact or associations.

A questioned sample has an uncertain source, while a known reference sample comes from an established source for comparison.

Direct transfer of material from one surface or object to another during contact.

Transfer of material to a recipient through an intermediate surface or object.

Transfer involving additional intermediate contacts beyond secondary transfer.

The length of time transferred material remains detectable on a recipient surface under particular conditions.

Fiber characteristics, fabric texture, activity, contact conditions, environmental exposure, and subsequent handling.

The frequency with which a material or characteristic occurs in relevant environments or populations.

A common fiber type generally provides less discriminating information than an unusual combination of well-characterized features.

The assessment of hair morphology and other properties to evaluate characteristics, possible origins, and comparisons.

The outermost layer of overlapping cells surrounding the hair shaft.

The main structural region of the hair shaft containing keratin and much of its pigment.

The central region of the hair shaft, which may be continuous, fragmented, discontinuous, or absent.

The approximate ratio of medulla diameter to total hair shaft diameter.

The values overlap and vary among species and hairs, so the index cannot establish origin by itself.

The end nearest the root or follicular attachment.

The end farthest from the root, often showing cutting, weathering, or other tip characteristics.

Possible forceful removal, although root appearance alone cannot reliably establish the circumstances of removal.

No. Microscopic similarities cannot establish that a hair came from one particular person to the exclusion of others.

Mitochondrial DNA, subject to sample condition and analytical limitations.

A natural or manufactured filament or staple material used in fabrics and related products.

A plant-derived fiber primarily composed of cellulose, such as cotton or flax.

An animal-derived fiber primarily composed of protein, such as wool or silk.

A manufactured fiber formed from synthesized polymers, such as nylon or polyester.

The difference in refractive index for light polarized in different directions through an anisotropic fiber.

It may help characterize the manufacturing process or fiber type and distinguish certain samples.

To measure and compare optical spectra of small fiber samples, helping evaluate colorant similarities or differences.

It reveals optical properties, including birefringence and extinction behavior, useful for distinguishing materials.

A crack extending outward from a point or region of applied force.

A curved crack developing around an impact region.

Radial cracks form Right angles on the Reverse side of the force, when the rule's conditions apply.

Glass type, support, loading conditions, and fracture complexity can limit its reliability.

It may indicate that the terminating crack formed later than the crack it encountered.

A measure of how much light changes speed and direction when passing through glass, useful as a comparison property.

Elemental composition can help distinguish glass fragments or assess their consistency with a possible source.

No. Different glass sources may share similar refractive indices.

A sequence of paint or coating layers deposited on a surface, potentially providing distinctive comparative characteristics.

The number, order, color, thickness, and composition of layers may help distinguish coating sources.

It can provide high-resolution imaging and information about the elemental composition of suitable paint components.

To characterize polymers by thermally breaking them into smaller products that are separated and analyzed.

A thermoplastic can generally soften when heated, while a cured thermosetting polymer forms a cross-linked structure that does not simply remelt.

Examination of physical, mineralogical, chemical, and biological characteristics of soil samples to assess similarities and differences.

Local geology, land use, environmental conditions, and introduced materials may produce distinctive combinations of soil characteristics.

The relative proportions of particles in different size ranges, such as sand, silt, and clay.

Mineral assemblages may help distinguish soils originating from different geological environments.

A correspondence between separated pieces based on complementary fracture surfaces, edges, or other continuous features.

Complementary fracture details can support a direct association, while many unrelated objects may share similar compositions.

No. The association must be interpreted considering background prevalence, possible secondary transfer, persistence, and other evidence.

The samples are distinguishable by elemental composition despite their similar refractive indices.

The chip is consistent with the vehicle's coating system, with the strength of association dependent on the discrimination of the observed features and analytical results.