Who packed the drugs? Improved DNA recovery and its impact on findings given activity-level propositions
Forensic Science International: Genetics, 2026
Authors
Journal
Forensic Science International: Genetics
Study Design
Addressed Question
Investigation of the effects of transfer type, substrate characteristics, and DNA extraction strategy on DNA yield, STR profiling performance, and resulting likelihood ratios given activity-level propositions.
Activity Context
Category
Specifications
Variables of Interest
Stringency of Control
Number of Individuals
20 (transfer study), 4 (paired extraction study)
Replicates per Individual and Condition
Transfer: 2 indirect zip-lock bags per participant + 1 direct-transfer bag for 13 participants, extraction study: 2 paired swabs per skin area
Nucleic Acid
Bodily Origin
Depositor & Contact
Depositor Characteristics
n.a.
Criteria for Shedder Status
n.a.
Previous Activities
All handling took place at least one hour after washing hands.
Contact Scenario
Indirect: investigator placed two sugar-filled zip-lock bags into each participant's personal backpack/purse, bags remained for 24 h and were manually agitated five times. Direct: 13 participants handled a new empty zip-lock bag by opening and closing it three times, then returned it in a clean envelope.
Primary Substrate
Primary Substrate Type
Direct transfer experiment: zip-lock bags. Indirect transfer experiment: backpack or purse
Primary Substrate Material
Deposit
Direct transfer experiment: Participant opened and closed a new zip-lock bag three times. Indirect transfer experiment: Personal backpacks or purses were used.
Delay
n.s.
Secondary Substrate
Secondary Substrate Type
Direct transfer experiement: none. Indirect transfer experiment: Zip-lock packs
Secondary Substrate Material
Secondary Substrate Contact
zip-lock bags were packed and placed inside each item by an investigator wearing gloves. The zip-lock bags were left for a 24-hour period. During this time, the bags were manually agitated five times
Further Transfer
n.a.
Sampling
Background DNA on Sampled Surface
Sampling Time
For direct transfer experiment: after 24h
Persistence
n.a.
Sampling Method
Sterile, moistened cotton swabs.
Sampling Area
Zip-lock size not specified. internal surface of personal bag: approximately 20 cm²
Laboratory Analysis
Extraction
Chelex extraction, a co-extraction protocol combining the QIAamp DNA Mini Kit and mirVana™ miRNA Isolation Kit, and Direct PCR
DNA Quantification
PowerQuant System
Input for Profiling
1 ng template, or 15 µL if 1 ng could not be reached
Profiling
Capillary electrophoresis was conducted on an Applied Biosystems 3500xL Genetic Analyser. The results were analysed using the GeneMapper ID-X Software version 1.6
Reference Samples
n.s.
Profile Interpretation and Mixture Analysis
Sub-source LRs were calculated with EuroForMix. When >2 alleles were observed at a marker, an additional unknown contributor was included in numerator and denominator.
RNA Data Interpretation
Housekeeping genes were used to assess cellular material. Markers included XIST (female marker), RPS4Y1 (male marker), HBB (blood marker), CD93 (blood marker), STATH (salvia marker), MUC4 (mucosa marker) and MMP11(menstrual blood marker). Analytical-threshold assessment.
Results
DNA Quantity
DNA quantities detected in samples from purses (average DNA concentration = 0.04 ng/µL). DNA quantities detected in samples from backpacks (average DNA concentration = 0.09 ng/µL). Extraction with co-extraction (average DNA concen tration=0.038 ng/µL). Extraction with Chelex 5% (average DNA concentration=0.0065 ng/µL)
Profile Quality
When comparing the genotyping results from Direct PCR (S1) with those from Chelex (2020 data), Direct PCR produced stronger profiles, with more alleles matching the donor and higher peak heights.
Parameter Used for Comparison
DNA concentration; total DNA quantity; RFU/POI RFU; sub-source Log10 LR; activity-level LR; DNAntransfer percentage; profile detection.
Summary of Results
Our results show that DNA transfer and recovery are affected by contact type, substrate, and item characteristics, with direct transfer and non-porous handled items producing the highest yields. Extraction approach also plays a critical role: a co-extraction protocol using QIAamp and mirVana™ kits outperformed Chelex, while Direct PCR provided a rapid but less efficient alternative.
Raised Questions
Need for larger and multi-laboratory datasets. Need to assess how laboratory methodology affects transfer/persistence distributions; need for transparency and standardisation of extraction methods. Need to validate the impact of extraction methods on activity-level transfer/persistence functions, particularly when historical cases are revisited.
Cautionary Remarks
N/A