The fingernails of Mary Sullivan: developing reliable methods for selectively isolating endogenous and exogenous DNA from evidence

The fingernails of Mary Sullivan, the last victim of the Boston Strangler, were examined to determine if any genetic information about the murderer could be obtained. The nails were extremely friable necessitating the development of new techniques for isolating and purifying DNA. DNA yields from nails were optimized by using a NaOH-based preparation technique, which was simple, efficient, and minimized handling. Methods for selectively and thoroughly removing exogenous material on nails were also developed through use of a species-specific PCR assay, wherein mitochondrial DNA from the nail could easily be differentiated from DNA of contaminating cells.     

The forensic analysis of thermal transfer printing

Thermal transfer printing refers to printing processes that utilize heat to produce an image by either physical or chemical means or by a combination of both. As the technology has improved and the supplies have become less expensive, the use of thermal printing in the personal and business markets has increased significantly. Specifically, dye diffusion thermal transfer and thermal mass transfer have become predominant in the production of counterfeit credit cards, drivers' licenses, and other types of documents produced on plastic media. Chemical analysis by means of thin layer chromatography (TLC) has proven to be useful in characterizing various types of inks (e.g., writing and inkjet inks). In this study, the authors examined 81 different samples that included a total of 54 printer samples (43 photographic prints on paper and eleven plastic card samples) and 27 printer ribbons. A new TLC method was developed and tested utilizing a solvent system (80% n-hexane, 3% methyl ethyl ketone, and 17% ethyl acetate) that is capable of producing excellent resolution.     

Quantification of forensic DNA from various regions of human teeth

When the use of traditional forensic identification methods such as fingerprints or dental radiographs is difficult or impossible, identification by DNA analysis has proven valuable. In situations such as explosions or airplane crashes, identification is even more difficult because human remains are often fragmented and may be commingled. Teeth are a useful source of DNA and can often survive extreme environmental conditions. However, teeth may be fragmented into several identifiable regions. Therefore it is important to determine if DNA is present in forensically significant yields in all regions of the tooth. The main objectives of this study were to determine which region(s) of the tooth contains quantifiable DNA, if all regions contain similar yields of DNA and whether there is enough DNA in all regions to justify DNA extraction from a found tooth fragment. Results demonstrate that there is sufficient quantity of DNA in the crown body, root body, and root tip to support DNA extraction. Additionally, the root body is the region with the highest yield of DNA. This information will aid forensic DNA analysts in producing a useful DNA profile in a timely and cost-effective manner.     

STR DNA typing: increased sensitivity and efficient sample consumption using reduced PCR reaction volumes

Improvements in detection limits/sensitivity and lower sample consumption are potential benefits of reducing PCR reaction volumes used in forensic DNA typing of crime scene samples. This premise was studied first with experimental mixtures and a nine-loci megaplex, which demonstrated stochiometric amplification and accurate detection. Next, adjudicated casework samples were subjected to amplification under 15 different template DNA to PCR reaction volume ratios. Reduction of PCR reaction volume and DNA down to 10 microL and 0.500 ng, respectively, produced identical profiles with the same signal intensity and heterozygous allele peak height ratio (HR). Reduction to 5 microL and 0.063 ng yielded HR values that were slightly affected in one to three STR loci. PCR reaction volume reduction can enhance detection and sensitivity while reducing the consumption of irreplaceable crime scene samples.