Complex Methodological Study of Forensic DNA Low-Template Analysis for Cold Case Resolution in Nigeria

Low-template DNA analysis techniques, including touch DNA recovery and probabilistic genotyping, offer transformative potential for resolving historical cold cases in which conventional DNA methods previously yielded insufficient results. This doctoral study investigates the application of low-template DNA analysis methodologies to cold case forensic investigations in Nigeria, developing optimised protocols for tropical environment DNA degradation contexts. A laboratory-based experimental design was employed, processing 120 archived cold case biological exhibits from the National Forensic Science Laboratory covering cases from 2005 to 2018, applying low-copy number PCR amplification, capillary electrophoresis, and probabilistic genotyping software, and assessing success rates, contamination risks, and interpretive complexity under conditions of advanced DNA degradation. The study develops an original tropical degradation correction model that adjusts probabilistic genotyping likelihood ratio outputs for Nigeria-specific temperature and humidity exposure histories. Successful genotyping profiles were obtained from sixty-three percent of previously unanalysable exhibits, with the tropical correction model improving likelihood ratio accuracy by a mean factor of 2.8. Stochastic effects including allelic dropout and drop-in were modelled empirically across five degradation severity categories. The study makes original methodological contributions to low-template DNA analysis practice in tropical forensic contexts and provides a scientifically validated protocol for cold case DNA reanalysis in Nigerian laboratories. Recommendations include a national cold case DNA review programme and the procurement of probabilistic genotyping software systems. Keywords: low-template DNA, cold case, probabilistic genotyping, tropical degradation, Nigeria.