Abstract

When DNA from a suspect is detected in a sample collected at a crime scene, there can be alternative explanations about the activity that may have led to the transfer, persistence and recovery of his/her DNA. Previous studies have shown that DNA can be indirectly transferred via intermediate surfaces and that DNA on a previously used object can persist after subsequent use of another individual. In addition, it has been shown that a person’s shedder status may influence transfer, persistence, prevalence, and recovery of DNA. In this study we have investigated transfer persistence and recovery on zip-lock bags and tape, which are commonly encountered in drug cases and how the shedder status of the participants influenced the results. A probabilistic framework was developed which was based on a previously described Bayesian network with case-specific modifications. Continuous modelling of data was used to inform the Bayesian networks and two case scenarios were investigated. In the specific scenarios only moderate to low support for Hp was obtained. Applying a continuous model based on the profile quality can change the LRs.

Highlights

  • IntroductionDNADirect transfer modelled from RFU E1dbag; personal bag (indirect transfer) was8

  • DNADirect transfer modelled from RFU E1dbag; personal bag was8

  • Likelihood ratios and mixture proportions were calculated using EuroForMix version 3.2.0 using propositions shown in in Equation (1), where U corresponds to unknown contributors, necessary to explain all alleles present

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Summary

Introduction

DNADirect transfer modelled from RFU E1dbag; personal bag (indirect transfer) was8. 8. Comparison ofwas probabilities of direct, indirect and background. TPPR for the zi modelled from RFU data andwas background was E2pbagtransfer. RFU from ;RFU adjusted k = 0.95 (the proportion of observations with no background) in order to scale results as modelled from RFU data and background was modelled from RFU d described in Supplementary Material S1. Justed k = 0.95 (the proportion of observations with no background) in order to scale r scribed in Supplementary

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