Forensic Entomology Lecture Notes (PDF)

Forensic Entomology LEC11 – Friday October 18th Foundations in Forensic Science  Test 1 Course Update LAB03 Forensic Anthropology LAB04 Forensic Entomology Forensic Entomology & Terminology Entomology – study of insects Succession – an ecological...

Forensic Entomology LEC11 – Friday October 18th Foundations in Forensic Science  Test 1 Course Update LAB03 Forensic Anthropology LAB04 Forensic Entomology Forensic Entomology & Terminology Entomology – study of insects Succession – an ecological sequence Oviparity – reproduction in which eggs are laid Necrophage – an eater of dead and/or decaying animals Carrion – dead and/or decaying animals Myiasis – parasitic infestation of live tissue by fly larvae Rearing – raising fly larvae to adulthood Larvae – immature form of insect, which emerges from eggs Pupae – stage between larval and adult stage, metamorphosis occurs Diapause – period of growth & development suspension Brief History Forensic Entomology 13th Century – Song Ci – Murder Case 19th Century Very soon after death Dr. Louis Bergeret (1955) – Skeletonized remains behind chimney Krahmer (1857) – Problems related to PMI estimates Weismann (1864) – Published development data for two flies Yovanovich (1888) and Megnin (1894) – First to examine succession on corpses 20th Century Horoszkiewicz (1907) – Modification of corpses by insects 1959-1983 – First uses in cases (Leclercq, and Nuorteva) 21st Century Acceptance in many countries judiciary proceedings Physical Changes soon after Death Algor Mortis Body temperature decreases Livor Mortis (Lividity) Skin colour reddens Rigor Mortis Stiffening of the muscles These provide good estimates until around 3 days Insects & Death Attracted soon after death Oviposition may not occur Colonization differs among insects 4 Categories: (Smith 1986) 1. Necrophageous species* 2. Predators or parasites* 3. Omnivorous species 4. Others Succession occurs in predictable sequence Succession of Corpse Blowflies First colonizers Attracted by odour produced during decomposition Ovisposition occurs in moist environments Orafaces/wounds Burial affects oviposition 30 cm too far Phoridae found in coffins Succession varies with season and geography Estimating Time Since Death Postmortem interval (PMI) 1 day – 1 month estimates Species ID First step to assess age Species grow at different rates in different environmental conditions Thermal summation Accumulated degree days Assumptions Temperature information Flies arrived and oviposit soon after death ADD linear relationship Myiasis did not occur Thermal Summation (ADD/ADH) Basic formula Number of hours from egg to adult multiplied by the temperature Species have unique developmental thresholds Each stage of development has its own degree time requirement Temperature is compared to local measures and modeled from time found Confounds: Maggot mass effect Species may have different thresholds geographically DNA Analysis ID of species is traditional done using morphology or rearing Very difficult with larvae! DNA used to ID species Crime scene larvae Museum samples Mitochondrial regions are used to compare between species Cytochrome oxidase – subunit I and/or II Species level comparison Human DNA in larval digestion Entomotixocology Analysis of larval shows toxic/drugs present Can be used to detect them in corpse Potential cause of death Any stage of larval development can be used May affect larval development Nuorteva (1982) – murder case Body found in rural Finland, area high in Mercury Mercury concentration found to be low in specimen Kintz et al. (1990) – reliability comparison Diptera larvae compared to dead tissue Entomotixocology Goff et al. (1997) – antidepressant presence Miller et al. (1994) – drug presences in empty pupa Goff et al. (1991) – drugs on rate of development Reared on liver/spleen of rabbits killed with lethal doses of cocaine/heroin Faster development of insects Bourel et al. (1999) – morphine in victim Underestimation of PMI by up to 24hrs Gunatilake and Goff (1989) – suicide with pesticide malathion PMI estimated at 5 days Likely delayed colonization Ongoing Research in Forensic Entomology Wrapping in blankets Seasonal/geographical differences Cave death (5°C) Oviposition timing during the day Diapause differs across temperature/time/species Decomposition in aquatic habitats completely different Case Study – Steven Truscott 1959 - Steven arrested (14 year old) charged with murder of friend and classmate Lynne Harper (12 year old) Opinion of attending pathologist – Dr. Penistan V died where body found between 7 & 7:45pm V’s genital area had suffered severe injury – sexual assault 2 Drs. examined Truscott on June 12 Testified to large lesions on penis Could have been caused by sexual assault on a young girl Estimated to be 2-4 days old Case Study – Steven Truscott Defence medical testimony challenged Crown’s medical expert Steven stood trial as adult, convicted to life 1966 – book published questioning the expert evidence on timing of death 1967 – Reference Re: Truscott at SCC – reviewed evidence and did not find fault 2001 – sought remedy from Min. of Justice – referred to OCA Expert evidence that earlier time frame evidence “ludicrous” based on stomach content and digestion analysis OCA allowed fresh evidence re: Dr. Penistan’s draft autopsy report and notes – findings not incompatible with death occurring during broader timeframe Docs had not been disclosed previously 15 Case Study – Steven Truscott OCA – 2007 – Truscott (Re:) Conviction miscarriage of justice Acquittal entered Examined expert evidence and determined Lack of impartiality Failure to disclose fact, documents, errors Use of scientific evidence with little probative value Over statement of probative value Use of potentially misleading language Over reliance on status of witness or science Inadequate scrutiny in cross-examination