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An Overview of Forensic Taphonomy

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An Overview of Forensic Taphonomy An Overview of Forensic Taphonomy David O. Carter, PhD Assistant Professor of Forensic Science Department of Entomology University of Nebraska-Lincoln, USA What is forensic taphonomy? taphos = grave, burial. -nomy = system of processes, rules, knowledge. A response to witness statements. Use of taphonomy: Identify the deceased Determine the cause and manner of death Estimate postmortem interval Locate clandestine graves Pathology Botany Anthropology Palynology Archaeology Mycology Entomology Ornithology Microbiology Meteorology Geoscience Molecular Biology Taphonomy Timeline PREHISTORY PRESENT Empirical Ecology Empirical Taphonomy Experimental Taphonomy Forensic Taphonomy Notable early forensic taphonomists Alexandre Lacassange—France Étienne Rollet—France Edmond Locard—France Jean-Pierre Mégnin—France Johann Casper—Germany 3rd edition published 1861 Haglund and Sorg 1997 Identify the Deceased Friction Ridges Friction ridge pattern = ridges + furrows Glands release sweat through the pores Begin to form between 10th & 12th week of pregnancy Fully formed by 24th week Are permanent and unique Can be well preserved when desiccated Fingerprint detail Level 1 Ridge Flow: direction that ridges flow Level 2 Ridge Events: breaks, splits and endings within the ridge pattern Level 3 Ridge Dimensions: size attributes and spatial location of ridges and pores. Level 1: Ridge Flow Ridge Flow is determined by the configuration and direction of ridges. This defines the “pattern type”. Three patterns: Arch Loop Whorl Level 2: Ridge Events 1) Ridge ending 2) Bifurcation 3) Dot 4) Short ridge 5) Enclosure dot bifurcation Ridge ending Short ridge enclosure Level 3: Ridge Dimensions Each ridge has a unique Width, shape, edge contour Pores vary in Number Shape Placement Fingerprint Comparisons Compare known to unknown Compare to fingerprints stored in AFIS and IAFIS AFIS Automated Fingerprint Identification System Can differ from agency to agency IAFIS Integrated AFIS US National System Forensic Biochemistry Genetic analysis Serology Autosomal DNA ABO typing Mitochondrial DNA Rhesus factor Y-STR Saliva Semen Cause and Manner of Death Cause of death Event or disease process that led to death (e.g. gunshot, blunt force trauma) Manner of death Natural Accidental Suicide Homicide Undetermined When is an autopsy done? (in Nebraska) 1. When Manner is: Accidental Suicide Homicide Undetermined 2. When the doctor wants it. Gunshot wounds Should be used for exclusion. Forensic Chemistry Toxicology Controlled Substances Blood alcohol Powders Vitreous humor Pills Cardiac blood Liquids Femoral blood Plants Organs Spores Postmortem Interval Postmortem Interval (PMI) The time elapsed since death. One 100% accurate estimate: Maximum PMI equals the time elapsed since the person was last seen alive and found dead. A collection of direct and indirect methods aim to narrow that estimate. Postmortem Interval What is used to estimate PMI? Rate methods: based on process that begins or ends at death; e.g. rigor mortis, maggot development. Accuracy tends to decrease as PMI increases. Concurrence methods: sequencing events that occurred at known times around death; e.g. phone records, emails, receipts, stopped watch. Why narrow the PMI estimate? Can help identify people Can help accept or reject alibi Can help reconstruct series of events Direct Estimates of PMI Algor mortis Believed that body cooled 1.5 degrees F per hour after death. Thermometer inserted 3-4” into the rectum. Must know: Temperature at death Duration of temperature plateau Algor mortis is not acceptable for estimating PMI Livor mortis Livor mortis usually observed between 20 and 120 minutes postmortem. Believed that livor mortis becomes fixed at 10-12 hours postmortem. Livor mortis is not acceptable for estimating PMI Rigor mortis Estimates: Becomes noticeable 3-4 hours postmortem Full rigor by 12 hours postmortem Lapsed by 36 hours postmortem Rigor mortis is not acceptable for estimating PMI Vitreous humor Measure of the concentration of potassium (K) over time 31% accurate, most often overestimates PMI Most accurate within 24 hours postmortem Vitreous humor is not acceptable for estimates of PMI Forensic Anthropology Indirect Estimates of PMI Degree Days Step 1: maximum temperature + minimum temperature 2 Step 2: subtract ‘base temperature’ base temperature = the lowest temperature at which that organism will grow. Accumulated Degree Days Sum each degree day Some taphonomists use Accumulated Degree Hours in an attempt to increase precision. Forensic Entomology Using the development of insects to estimate PMI Using the succession of insects to estimate PMI Key to understanding this use is through understanding the Degree Day Needed for Forensic Species of blow flyEntomology (Diptera: Calliphoridae) Age of blow fly Temperature at crime scene Growth rate of blow fly species Egg 1st stage 2nd stage 3rd stage pupa ADDs 374 418 572 1012 3014 Hours at 22 17 19 26 46 137 °C Grassberger and Reiter (2001) Forensic Sci Int 120:32-36 Gravesoils Probably the best way to estimate PMI once maggots have migrated. Based on concentration of chemicals in gravesoil and accumulated degree days. At present, gravesoil PMI estimates use base temperature of 0 °C. Not certain if this is correct. nutrient concentration 600 500 cadaver 1 - 400 ammonium soilkg 1 - potassium 300 chloride 200 calcium ppm nutrient g nutrientppm 100 0 0 1000 2000 3000 4000 5000 Accumulated degree days Vass et al. (1992) J Forensic Sci 37:1236- 1253 Volatile Fatty Acids 16 14 1285 ADDs = no more 12 VFAs cadaver 1 - 10 propionic soil kg 1 8 n-butyric - iso-valeric 6 mmol VFA VFA mmolg 4 2 0 0 200 400 600 800 1000 1200 Accumulated degree days Vass et al. (1992) J Forensic Sci 37:1236- 1253 Vass’s rule of thumb for PMI For pre-skeletonized bodies 1285 degree days = end of volatile fatty acid release 1285 ÷ average temperature (°C) on day of discovery = approximate maximum PMI Consider average temperature of 22 °C: 1285/22 = 58.4 58.4 days = maximum PMI Newest PMI equations • Aboveground Decomposition 1285 x (decomposition/100) 0.0103 x temperature x humidity • Belowground Decomposition 1285 x (decomposition/100) x 4.6 x adipocere 0.0103 x temperature x soil moisture ninhydrin-reactive nitrogen Ninhydrin-reactive nitrogen is protein peptide amino acids ammonium • An increase in NRN occurs after 320 ADDs regardless of death in winter or summer Gravesoil NRN can remain elevated for 1 year. Gravesoil pH can be significantly lower for 1 year. Locating Clandestine Graves Hunter et al. 1996 Dupras et al. (2005) Dupras et al. (2005) Dupras et al. (2005) Similarities between Crime Scene Investigation and Archaeology 1st responder is responsible for success One chance to recover information: destructive process Documentation is critical Reconstruction based on physical evidence Enhancement used to locate objects Ground Penetrating Radar, resistivity, thermal imaging, etc. Reports produced References Dupras TL et al. (2005) Forensic Recovery of Human Remains: Archaeological Approaches. CRC Press. Gunn A (2009) Essential Forensic Biology. 2nd Edition. Wiley- Blackwell. Houck MM, Siegel JA (2010) Fundamentals of Forensic Science. 2nd Edition. Academic Press. Hunter J et al. (1997) Studies in Crime: An Introduction to Forensic Archaeology. Batsford. James S, Nordby JJ (2009) Forensic Science: An Introduction to Scientific and Investigative Techniques. 3rd Edition. CRC Press. David O. Carter, PhD Assistant Professor of Forensic Science Department of Entomology University of Nebraska-Lincoln, USA [email protected].
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