Zeitschrift für forensische Forschung

Currently, Short Tandem Repeats (STRs) based forensic DNA typing technology is being internationally used in solving a diverse range of forensic cases, and presently, forensic DNA tests employ Polymerase Chain Reaction (PCR) and Capillary Electrophoresis (CE) based fragment analysis methods to detect length variation in STRs. The quality of STR-based DNA profiles from challenging samples depends on the yield and quality of DNA. The yield of DNA predominantly depends upon the method used for DNA extraction. DNA extraction is the first and perhaps most important step in any Forensic DNA analysis. Any specific method can never be thought of to be convenient for all types of samples. Still, Phenol Chloroform Isoamyl Alcohol (PCIA) method which is called the organic extraction method has been proven to be useful for a wide variety of forensic samples ranging from the simplest saliva or blood to complex bone and teeth samples. In the present study, we compared the performance and DNA yield of four different DNA extraction methods- EZ1Advanced XL, AutoMate Express TM, PCIA, and chelax method on broad range of samples commonly encountered in forensic casework and their compatibility with present-day STR based capillary electrophoresis typing. The mean value of DNA yield was found 114.21 ng/μl, 49.028 ng/μl, 35.485 ng/μl, 4.694 ng/μl by PCIA, AutoMate Express TM, EZ1Advanced XL, and Chelex DNA extraction methods, respectively. Conclusively, the highest yield was observed from all the tested samples from the PCIA method.

During drive-by shooting, police barricade, or armed bank robbery incidents, bullets hitting from a right angle onto a hard surface (car metal, concrete, or brick walls) usually turn into highly deformed bullets (HDB) on the ground due to the heavy impact. From the perspective of forensic practice, these HDBs bear little information due to the fact that there is only one or two rifling’s (lands/grooves) usable on the HDBs for the firearm examination. While the number of rifling is one of the standards or criteria for a bullet-weapon determination, an HDB with only one or two visible lands or grooves renders it little evidential value for identification. With a quasi-experimental design and a purposive sampling, two pairs of highly deformed jacked bullets (9 mm and .30) and one pair of highly deformed lead bullet (.38) were selected for testing and calculating. Using a palm-sized digital device, the study proposes a new mathematical formula that allows calculating the number of rifling on HDBs fired from pistols or revolvers. This new approach is able to provide a real-time method of determining the number of rifling’s on the HDBs to improve crime scene investigations as well as later lab work for bullet-weapon identification.