Secondary Transfer
Definition
The movement of a glass fragment from a primary surface (which contacted the broken glass) to a secondary surface (which contacted the primary surface but not the broken glass directly); a critical consideration when assessing the evidential significance of glass fragments on a suspect.
- Definition
- Transfer via an intermediate person or object, not direct contact between the final surface and the original source.
- Evidence types affected
- DNA, GSR particles, glass, paint, and fibers.
- Forensic implication
- Presence of trace evidence alone does not prove direct involvement in an event.
Common questions
How does secondary transfer happen?+
Secondary transfer occurs when trace material moves from a primary surface (where it was directly deposited, like a shooter's hands) to a secondary surface through contact with an intermediate person or object. For example, GSR particles can transfer from a shooter to someone else via handshaking, or glass fragments can move from a broken window to a suspect via contact with someone who touched the broken glass directly.
Why is secondary transfer important in forensic evidence?+
Secondary transfer is a documented alternative explanation for trace evidence on a suspect or surface. Finding DNA, GSR particles, or glass fragments does not necessarily prove direct involvement in the crime, since these materials can spread through ordinary contact. Examiners must assess secondary transfer as a rival hypothesis before concluding guilt or innocence.
Can any type of trace evidence undergo secondary transfer?+
Yes. Touch DNA, gunshot residue, glass fragments, paint, and fibers have all been documented to spread through secondary transfer. The mechanism is the same across all materials: already-transferred evidence moves from one surface to another without the original source ever touching the final surface.
Related terms
- Bayesian Likelihood Ratio (LR)
- The statistical framework that evaluates glass-fragment evidence by comparing the probability of the observed fragment population assuming contact with the source glass...
- 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...
- Touch DNA
- Minute quantities of epithelial cells transferred by skin contact with a surface, without leaving a visible stain. Collected by swabbing contact points...
- 3R Rule
- The fracture-analysis mnemonic: Radial cracks form at Right angles to the Reverse (far, non-impact) side of the glass. Applied to the fracture...
- 5% HNO3 Swab
- A cotton or polyester swab pre-wetted with 5% nitric acid, used to collect dissolved GSR for atomic absorption spectrometry or ICP-MS. Recovers...
- Allele Drop-in
- Appearance of a low-level allele in a PCR product from stochastic amplification of a contaminant molecule. More common in low-template reactions where...
- Allele Drop-Out
- Failure of one allele at a heterozygous locus to amplify in a low-template PCR reaction, producing an apparent homozygote. Increases dramatically below...
- Antimony Sulphide
- Sb2S3, the primary fuel in conventional primer formulations, burning rapidly in the presence of oxygen released by barium nitrate during ignition.
- ASTM E1588
- ASTM International standard practice for gunshot residue analysis by scanning electron microscopy with energy-dispersive spectrometry. Defines particle classification (characteristic, consistent-with, indicative), morphology...
- ASTM E1967
- The ASTM International standard for forensic glass RI measurement; specifies three acceptable methods (automated, semi-automated, manual), minimum precision of ±0.0001 RI units,...
- ASTM E2927
- Standard test method for the determination of trace elements in glass samples using LA-ICP-MS; specifies the element suite, calibration standards (NIST SRM...
- Automated Particle Search (APS)
- A software-driven SEM mode that scans the entire stub surface using backscattered electron contrast, flags particles above an atomic-number threshold, and triggers...
Explained in these topics
- Botanical Evidence: An OverviewThe movement of botanical material from one person or object to another without direct contact with the original source location. Secondary transfer is a key a...
- Glass Comparison: RI, Density and LA-ICP-MSThe transfer of a glass fragment from a primary contact surface to a secondary surface without direct contact between the secondary surface and the broken glas...
- Glass Fragmentation and Direction-of-Force AnalysisThe movement of a glass fragment from a primary surface (which contacted the broken glass) to a secondary surface (which contacted the primary surface but not...
- GSR Sampling Protocols, Persistence and Secondary TransferThe movement of GSR particles from a primary-deposit surface (a shooter's hands or clothing) to a secondary person or surface through physical contact. Documen...
- Gunshot Residue: Three-Component Particles and SEM-EDXThe deposition of GSR particles onto a person or surface that did not directly fire a weapon, via contact with a primary source (the shooter or the fired weapo...
- Interpreting Biological Evidence in CourtThe movement of biological material from one surface to another through an intermediate contact, rather than direct contact with the person of interest. A DNA...
- Locard's Exchange Principle and Trace TransferAlready-transferred material moving on to a further surface without the original source ever touching that surface. A handshake can carry another person's fibr...
- Paint Databases (PDQ, EUCAP) and Comparison CaseworkPaint that reaches the questioned surface via an intermediate object rather than direct contact; a recognised cross-examination challenge to transfer-mechanism...
- Touch DNA and Trace Biological MaterialThe indirect movement of biological material from a primary surface (where direct contact occurred) to a secondary surface via an intermediary. In touch DNA co...
- Touch DNA, Hair, Bone, Teeth and Challenging SubstratesDeposition of cells (and their DNA) from a donor onto a surface they never directly contacted, via an intermediate person or object. A recognised source of mis...