## Investigation of Choice in Rape Cases ### Role of DNA Profiling **Key Point:** DNA profiling (DNA fingerprinting) is the gold standard and most specific investigation for establishing the identity of the perpetrator and creating a definitive link between the perpetrator and the crime scene. ### Why DNA Profiling is Superior | Aspect | DNA Profiling | Other Tests | |--------|---------------|-------------| | **Specificity** | Virtually 100% (1 in 10 billion) | Low (only presumptive) | | **Identifies perpetrator** | Yes, uniquely | No | | **Admissible in court** | Yes, gold standard | Limited legal value | | **Time sensitivity** | Can detect up to 72 hours | Motile sperm: 6–8 hours only | | **Contamination risk** | Minimal with proper collection | High with environmental factors | ### Timing Considerations **High-Yield:** At 18 hours post-assault, motile spermatozoa are unlikely to be found (motility persists only 6–8 hours in vaginal environment). DNA from semen remains stable and detectable for days if properly preserved. **Clinical Pearl:** DNA evidence collected from the victim can be compared with the suspect's DNA profile to establish guilt or innocence with near-certainty. This forms the cornerstone of modern forensic medicine in sexual assault cases. ### Role of Other Tests - **Wet mount microscopy:** Useful for *presence* of semen but not identity; motile sperm disappear within 6–8 hours - **Acid phosphatase test:** Presumptive test for seminal fluid; not specific to identity - **Blood grouping:** Cannot identify the perpetrator; only narrows population **Mnemonic:** **DNAS** — DNA is the Definitive, Nationally Accepted, Specific investigation for perpetrator identification [cite:Parikh Textbook of Medical Jurisprudence & Toxicology Ch 26] 
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