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Secondary DNA Transfer


How Did the DNA Get There?
Advancements in DNA testing are overall fantastic, it is important to be aware of the limitations in terms of determining how the trace DNA arrived at a location and how long it might have been there.
It can NOT be assumed that if your DNA is located at a crime scene you must have been present, and you probably committed the crime.
Investigators must look at other evidence surrounding the case, both circumstantial and physical
Considerations must be given to the fact that the DNA could have arrived on the evidence innocently or it could have been transferred via a secondary transfer event.



2016 Study
Could Secondary DNA Transfer Falsely Place Someone at the Scene of a Crime?

Cale, C. M., Earll, M. E., Latham, K. E., & Bush, G. L. (2016). Could Secondary DNA Transfer Falsely Place Someone at the Scene of a Crime?. Journal of forensic sciences, 61(1), 196–203. https://doi.org/10.1111/1556-4029.12894


2017 Published Study
An investigation into the deposition and persistence of directly-and indirectly-transferred DNA on regularly-used knives

Meakin, G. E., Butcher, E. V., van Oorschot, R., & Morgan, R. M. (2017). Trace DNA evidence dynamics: An investigation into the deposition and persistence of directly- and indirectly-transferred DNA on regularly-used knives. Forensic science international. Genetics, 29, 38–47. https://doi.org/10.1016/j.fsigen.2017...


Results
In three pairings of volunteers, after the handshaking and stabbing events, alleles that could be attributed to the respective handshakers profiles were detected as partial minor profiles, equating to ~10% of the profiles recovered.
For the fourth pairing of volunteers, only complete single-source DNA profiles matching the regular user’s profile were recovered.



Important Note
When indirectly-transferred handshaker DNA was detected, it declined with increasing time between DNA deposition and recovery.


Summary
This data provides an initial insight into the detection and persistence of directly-and indirectly-transferred DNA that extend the data already available on forensic DNA transfer.
These results suggest that the sooner an item is sampled after an offence has occurred, the greater the chance of recovering indirectly-transferred DNA, which has implications for forensic reconstructions.


Highlights
DNA recovery from similar regularly-handled single user knives varies among users.
DNA from a user’s romantic partner can be deposited indirectly via the user’s hands.
Non-depositor DNA on single user knives is minor profile, even after handshaking.
Persistence of directly- and indirectly-deposited DNA declines over time.


Link to Lecture Slides: https://drive.google.com/file/d/11pXv...

*Due to the description character limit the full work cited for "Upper Limbs" can be viewed at... https://drive.google.com/file/d/1_XTa...