Uticaj različitih načina pranja okrvavljene tkanine na ekspertizu tragova krvnih mrlja i rezultat DNK analize

In practice, there are often various attempts to remove traces of blood from items in order to conceal a crime. In the study, samples of bleached cotton fabric (360 samples in total) were used, which were then washed through one of six different washing cycles. After a period of time the samples were analyzed. The macroscopic appearance of the samples, the reaction of the samples to chemical tests for the presence of blood, quantity (concentration) of DNA, DNA degradation index and DNA profiles were analyzed. Machine washing at a temperature of 95 and 60oC using detergent can remove visible but not invisible traces of bloodstains up to 10 days old, while bloodstains aged 30 days cannot be removed in one washing cycle. Regardless of the method of washing, after washing, the visible remaining part of the bloodstain will be the dominant circumferential edge of the area of the original bloodstain. Comparative analysis with the results of DNA analysis revealed that washing older bloodstains from the cotton fabric makes it easier to remove the DNA, while the visual feature of bloodstains originating from hemoglobin is more difficult to remove in older bloodstains. The statistical significance of the DNA degradation index of the material remaining in the bloodstains after washing was revealed at the same time concerning the washing temperature (95 and 60oC) and the application of the detergent, with the existence of a synergistic enhancing effect of these two factors on the DNA degradation index. This pattern is completely absent in the sample group washed at 30oC. By comparing the results, it was concluded that different experimental conditions in this study, namely water temperature and detergent, affect different target parts of DNA (different STR loci) and thus accelerate the degradation of DNA. Therefore, early-stage DNA degradation does not occur uniformly in all parts of the genetic material, but this effect is lost with the passage of time and degradation becomes more alike in all parts of the DNA. This research identifies certain new scientific facts that provide forensic experts with a new perspective on concealing the traces of crime