An Overview of Forensic Taphonomy

Transcription

1 An Overview of Forensic Taphonomy David O. Carter, PhD Assistant Professor of Forensic Science Department of Entomology University of Nebraska-Lincoln, USA

2 What is forensic taphos = grave, burial. taphonomy? -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

3 Pathology Anthropology Archaeology Entomology Microbiology Geoscience Botany Palynology Mycology Ornithology Meteorology Molecular Biology

4 Taphonomy Timeline PREHISTORY Empirical Ecology PRESENT Empirical Taphonomy Experimental Taphonomy Forensic Taphonomy

5 Notable early forensic taphonomists Alexandre Lacassange France Étienne Rollet France Edmond Locard France Jean-Pierre Mégnin France Johann Casper Germany

6 3 rd edition published

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9 Haglund and Sorg 1997

10 Identify the Deceased

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12 Friction Ridges Friction ridge pattern = ridges + furrows Glands release sweat through the pores Begin to form between 10 th & 12 th week of pregnancy Fully formed by 24 th week Are permanent and unique Can be well preserved when desiccated

13 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.

14 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

15 Level 2: Ridge Events 1) Ridge ending 2) Bifurcation 3) Dot 4) Short ridge 5) Enclosure

16 dot Ridge ending bifurcation Short ridge enclosure

17 Level 3: Ridge Dimensions Each ridge has a unique Width, shape, edge contour Pores vary in Number Shape Placement

18 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

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28 Forensic Biochemistry Genetic analysis Autosomal DNA Mitochondrial DNA Y-STR Serology ABO typing Rhesus factor Saliva Semen

29 Cause and Manner of Death

30 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

31 When is an autopsy done? 1. When Manner is: Accidental Suicide Homicide Undetermined 2. When the doctor wants it. (in Nebraska)

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38 Gunshot wounds

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40 Should be used for exclusion.

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45 Forensic Chemistry Toxicology Blood alcohol Vitreous humor Cardiac blood Femoral blood Organs Controlled Substances Powders Pills Liquids Plants Spores

46 Postmortem Interval

47 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.

48 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, s, receipts, stopped watch. Why narrow the PMI estimate? Can help identify people Can help accept or reject alibi Can help reconstruct series of events

49 Direct Estimates of PMI

50 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

51 Livor mortis Livor mortis usually observed between 20 and 120 minutes postmortem. Believed that livor mortis becomes fixed at hours postmortem. Livor mortis is not acceptable for estimating PMI

52 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

53 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

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55 Forensic Anthropology

56 Indirect Estimates of PMI

57 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.

58 Accumulated Degree Days Sum each degree day Some taphonomists use Accumulated Degree Hours in an attempt to increase precision.

59 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

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65 Needed for Forensic Entomology Species of blow fly (Diptera: Calliphoridae) Age of blow fly Temperature at crime scene Growth rate of blow fly species Egg 1 st stage 2 nd stage 3 rd stage pupa ADDs Hours at 22 C Grassberger and Reiter (2001) Forensic Sci Int 120:32-36

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68 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.

69 ppm nutrient g-1 soil kg-1 cadaver Vass et al. (1992) J Forensic Sci 37: nutrient concentration ammonium potassium chloride calcium Accumulated degree days

70 mmol VFA g-1 soil kg-1 cadaver Volatile Fatty Acids ADDs = no more VFAs propionic n-butyric iso-valeric Accumulated degree days Vass et al. (1992) J Forensic Sci 37:

71 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 = days = maximum PMI

72 Newest PMI equations Aboveground Decomposition 1285 x (decomposition/100) x temperature x humidity Belowground Decomposition 1285 x (decomposition/100) x 4.6 x adipocere x temperature x soil moisture

73 ninhydrin-reactive nitrogen Ninhydrin-reactive nitrogen is protein peptide amino acids ammonium

74 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.

75 Locating Clandestine Graves

76 Dupras et al. (2005) Hunter et al. 1996

77 Dupras et al. (2005)

78 Dupras et al. (2005)

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80 Similarities between Crime Scene Investigation and Archaeology 1 st 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

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82 References Dupras TL et al. (2005) Forensic Recovery of Human Remains: Archaeological Approaches. CRC Press. Gunn A (2009) Essential Forensic Biology. 2 nd Edition. Wiley- Blackwell. Houck MM, Siegel JA (2010) Fundamentals of Forensic Science. 2 nd 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. 3 rd Edition. CRC Press.

83 David O. Carter, PhD Assistant Professor of Forensic Science Department of Entomology University of Nebraska-Lincoln, USA