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
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 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