Understanding a Common Misinterpretation in Sexual Assault Cases
The difference between detecting semen and attributing DNA to it
Presumptive tests are not confirmatory
Confirmatory testing has limits
Why semen detection does not equal DNA attribution
- incomplete separation of sperm and non-sperm cells
- loss of material during processing
- mixed DNA results despite attempted separation
- low-level DNA profiles that do not clearly indicate origin
Why TIME SINCE INTERCOURSE (TSI) FURTHER COMPLICATES
Why this distinction matters in court
- DNA attributed to semen may suggest recent sexual activity
- DNA from skin cells or indirect transfer may support alternative explanations
- mixed-source DNA complicates assumptions about timing and activity
A common source of misunderstanding
- the presence of semen does not automatically identify a contributor
- the presence of a DNA profile does not automatically indicate biological source
- likelihood ratios address whose DNA may be present, not how it was deposited
The role of independent forensic review
- whether semen identification was presumptive or confirmatory
- whether sperm cells were definitively observed
- whether differential extraction was attempted and successful
- whether the DNA profile can or cannot be reasonably attributed to semen
- what alternative explanations remain scientifically plausible
Final observation
