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An Overview of Forensic Taphonomy David O. Carter, PhD Assistant Professor of Forensic Science Department of Entomology University of Nebraska-Lincoln, USA
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
Anthropology
Archaeology
Entomology
Microbiology
Geoscience
Botany
Palynology
Mycology
Ornithology
Meteorology
Molecular Biology
Taphonomy Timeline
Empirical Ecology
Empirical Taphonomy
Experimental Taphonomy
Forensic Taphonomy
PREHISTORY PRESENT
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 1Ridge Flow: direction that ridges flow
Level 2Ridge Events: breaks, splits and endings within the ridge
pattern
Level 3Ridge 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
enclosure
Ridge
ending
dot
bifurcation
Short ridge
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 analysisAutosomal DNA
Mitochondrial DNA
Y-STR
SerologyABO typing
Rhesus factor
Saliva
Semen
Cause and Manner of Death
Cause of deathEvent or disease process that led to death (e.g. gunshot, blunt
force trauma)
Manner of deathNatural
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
Blood alcohol
Vitreous humor
Cardiac blood
Femoral blood
Organs
Controlled Substances
Powders
Pills
Liquids
Plants
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 IntervalWhat 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
EntomologySpecies of blow fly (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
°C
17 19 26 46 137
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
0
100
200
300
400
500
600
0 1000 2000 3000 4000 5000
pp
m n
utr
ien
t g-1
so
il kg-1
ca
da
ve
r
Accumulated degree days
ammonium
potassium
chloride
calcium
Vass et al. (1992) J Forensic Sci 37:1236-
1253
Volatile Fatty Acids
0
2
4
6
8
10
12
14
16
0 200 400 600 800 1000 1200
mm
ol V
FA
g-1
so
il k
g-1
cad
av
er
Accumulated degree days
propionic
n-butyric
iso-valeric
1285 ADDs = no more
VFAs
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 adipocere0.0103 x temperature x soil moisture
ninhydrin-reactive nitrogen
Ninhydrin-reactive nitrogen is
protein
peptide
amino acids
ammonium
Gravesoil NRN can remain elevated for 1 year.
Gravesoil pH can be significantly lower for 1 year.
• An increase in NRN occurs after 320 ADDs regardless of death in winter
or summer
Locating Clandestine Graves
Dupras et al. (2005)
Hunter et al. 1996
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
