Results of the 2003-2004 GEP-ISFG collaborative study on mitochondrial DNA: focus on the mtDNA profile of a mixed semen-saliva stain

We report here a review of the seventh mitochondrial DNA (mtDNA) exercise undertaken by the Spanish and Portuguese working group (GEP) of the International Society for Forensic Genetics (ISFG) corresponding to the period 2003-2004. Five reference bloodstains from five donors (M1-M5), a mixed stain of saliva and semen (M6), and a hair sample (M7) were submitted to each participating laboratory for nuclear DNA (nDNA; autosomal STR and Y-STR) and mtDNA analysis. Laboratories were asked to investigate the contributors of samples M6 and M7 among the reference donors (M1-M5). A total of 34 laboratories reported total or partial mtDNA sequence data from both, the reference bloodstains (M1-M5) and the hair sample (M7) concluding a match between mtDNA profiles of M5 and M7. Autosomal STR and Y-STR profiling was the preferred strategy to investigate the contributors of the semen/saliva mixture (M6). Nuclear DNA profiles were consistent with a mixture of saliva from the donor (female) of M4 and semen from donor M5, being the semen (XY) profile the dominant component of the mixture. Strikingly, and in contradiction to the nuclear DNA analysis, mtDNA sequencing results yield a more simple result: only the saliva contribution (M4) was detected, either after preferential lysis or after complete DNA digestion. Some labs provided with several explanations for this finding and carried out additional experiments to explain this apparent contradictory result. The results pointed to the existence of different relative amounts of nuclear and mtDNAs in saliva and semen. We conclude that this circumstance could strongly influence the interpretation of the mtDNA evidence in unbalanced mixtures and in consequence lead to false exclusions. During the GEP-ISFG annual conference a validation study was planned to progress in the interpretation of mtDNA from different mixtures.     

Death in bathtub revisited with molecular genetics: a victim with suicidal traits and a LQTS gene mutation

A 44-year-old woman with a medical history of mental disorders and previous suicidal behaviour was found in a bathtub and pronounced death few minutes later despite of resuscitation attempts. After police investigation and on the basis of autopsy findings, the death was classified as suicide drowning. Retrospective examination of clinical data revealed, a prolonged rate-corrected QT-interval (QTc: 468 ms) 3 months before death. Post-mortem (PM) DNA analysis disclosed KCNH2(FIN) mutation for the long-QT syndrome (LQTS). The value of PM molecular screening for LQTS is emphasised, especially for victims of putative drowning.     

“He's guilty!”: Investigator Bias in Judgments of Truth and Deception

Detecting deception is an inherently difficult task, but one that plays a critical role for law enforcement investigators in the interrogation room. In general, research has failed to indicate that performance in this domain is improved by training or prior experience. A signal detection framework is applied to the paradigm to better conceptualize the influence of these two factors. We found that although neither factor influenced discrimination accuracy, there was an effect on response bias such that training and prior experience appeared to increase the likelihood of responding deceit as opposed to truth. This investigator bias was observed both in a review of the literature and in this study of North American law enforcement investigators who took part in a forensically based deception-detection task. Possible theoretical mechanisms and practical implications of these findings are discussed.     

Diagnosis of drowning by investigation of left heart blood

Nineteen cases of drowning and fourteen controls were studied in order to find pulmonary alveolar macrophages, diatoms and various, mainly crystalline, dirt particles in left heart blood. The results show promise for the development of a new diagnostic method for forensic purposes.