ConstructingConstructing (and Deconstructing) ( g)

the Postmortem Interval

H Gill Ki Ph D D ABFAH. Gill-King, Ph.D., D-ABFALaboratory of Forensic Anthropology

C t f H Id tifi tiCenter for Human IdentificationGraduate School of Biomedical Sciences

Uni ersit of North Te asUniversity of North Texas

General approaches

Rate methods / Death is a process, not anRate methods / Death is a process, not an event

Concurrence methods / One event fixed in ti l t d ith thtime correlated with another

Estimation of the postmortem intervalEstimation of the postmortem interval remains a persistent challenge , and one of the most important in forensic science.

1 Inclusion and exclusion of suspects1. Inclusion and exclusion of suspects2. Civil applications3 Establishing medicolegal significance3. Establishing medicolegal significance

Sources of evidence

1. Corporeal / evidence from the body2 i l / l2. Environmental / contextual3. Anamnestic

Progression of eventsProgression of events

1. Fresh /early (supravital period)2 Intermediate (putrefaction decomposition)2. Intermediate (putrefaction, decomposition)3. Extended (aerobic decay, weathering)

All bodies will pass through this progression, l h h h d ll i i h d halthough the dwell time in each stage and the

overall time may vary considerably.

IntervalsIntervals

Short interval (hours to days) -- irreversible circulatory arrestirreversible circulatory arrest-- global ischemia

autolysis follows rate of glycolysis and-- autolysis follows rate of glycolysis and corrresponding drop in pHdi ti f b -- disruption of membrane pumps

-- observable changes

Short interval contd.

Rigor mortis – Generalized stiffening of theRigor mortis Generalized stiffening of theMuscles / onset 2-4 hrs, resolution 24-84 hrs.

Onset and duration will be affected by

1.Agonal state-- hyperthermia / hypothermiahyperthermia / hypothermia-- metabolic e.g. diabetes, electrolyte

imbalance, lactic acidosisba a ce, act c ac dos s-- dehydration

2. Body composition. ody co pos o3. Ambient conditions at the scene

Additional problemsAdditional problems

1 S bjecti it in staging1.Subjectivity in staging2.Lack of contextual information from the

scene

Use of rigor mortis as the sole indicator ofUse of rigor mortis as the sole indicator of PMI should be avoided.

Short interval contd.

Al ti (cooling)Algor mortis (cooling)

Dead bodies do not follow Newton’s ExponentialNewton s Exponential cooling curve for a variety of reasonsof reasons.

Cooling variables

1. Strong radiation (e.g. solar or proximity to a heating device))

2. Uncertain alternating temperatures (e.g. HVAC system, windows open, etc.)

3 If o tdoors e tensi e climatic changes hich do not3. If outdoors, extensive climatic changes which do not allow for estimates of representative mean values.

4. General hypothermia or malignant hyperthermia.

5. Remains believed to have been transported.

6 Body composition6. Body composition

7. Clothingg

8. Ambient temperature higher than 37C

9. Convection and humidity

10. Bodies are not uniformly dense. Core to shell andshell to environment transfer produce a plateau withshell to environment transfer produce a plateau withsignificant resulting variations during the first 6 hrs.

Livor mortis (hypostasis)

1. Visible soon after death. 2 Easily ‘blanched’ for a few hours2. Easily blanched for a few hours.3. Usually ‘fixed’ and cannot be blanched within 8-12

hrs. 4. Determined by body position for the first few hours

following death

Quantitative measures of hypostasis, (colorimetric and )hemoglobin concentration), correlate with PMI, but are not 

statistically validated.  Factors which affect  quantification include  1. Pigmentationg2. Subcutaneous fat distribution / body composition3. Agonal temperature4 Ambient temperature4. Ambient temperature

Other supravital rate methods

1. Neuromuscular induction -- iridial responsiveness to chemical stimuli-- electrical stimulation of mimetic and thenar muscles

2. Ocular changescorneal opacity-- corneal opacity

-- segmentation (“boxcaring”) of retinal vessels3. Transit time of gastric contents3. Transit time of gastric contents4. Vitreous analytes

-- K+-- creatinine-- urea / glucose

h thi / 3 th t i-- hypoxanthine / 3 methoxytyramine

Eye Changes1 “Boxcaring” of retinal vessels ½ hr1 “Boxcaring” of retinal vessels ½ hr1. Boxcaring of retinal vessels ½ hr

eyes > open closed2. Corneal film mins several

1. Boxcaring of retinal vessels ½ hreyes > open closed

2. Corneal film mins several hrs

3. Scleral discoloration mins several hrs

hrs 3. Scleral discoloration mins several

hrshrs4. Corneal cloudiness < 2 hrs 12-24

hrs5 C l it 3rd PM d

hrs4. Corneal cloudiness < 2 hrs 12-24

hrs5 C l it 3rd PM d5. Corneal opacity 3rd PM day5. Corneal opacity 3rd PM day

Food in Stomach

VariationsLiquid faster than semisolid faster than solid- Liquid faster than semisolid faster than solid

- Emotional state – psychogenic pylorospasm = delay for several hoursfor several hours

- Hypermotility – 6-7 ft/hr…reaches caecum in 3 – 3.5 hrs (normal = 6-8 hrs)hrs (normal 6 8 hrs)

- CNS / spinal damage

mol/L

mmol/L

K+ [m

m

K+  [m

Intermediate postmortem intervalIntermediate postmortem interval(days to weeks)

Supravital changes at endpointGreater emphasis on sceneGreater emphasis on scene Increased reliance on structural changesExpect wider time bracketsExpect wider time bracketsChanges are subjective / non-quantifiable

Decompositional / Putrefactive changesSlippage – Breakdown at intercellular junctions

Separation at papillary line

Marbling - Heme degradation + H2S Ferrous sulfide

Bulla(e) – Capillary fluid / plasma between skin layers

Bloating – Enteric anaerobes and facultatives ramp up fermentative rate. Increased rate of hydrolysisof protein, lipid, carbohydrate substrates

P fl id A t l i f GI d i t t tPurge fluid – Autolysis of upper GI and respiratory tracts

SlippageBullaeBullaeMarblingBl tiBloatingPurge fluid

I t t ti bj t tInterpretation subject to:Ambient temperature (Q10 rule)Ambient temperature (Q10 rule)Ambient Moisture (Influence on bacterial activity)Age of individual (Development of enteric flora)Age of individual (Development of enteric flora)Agonal state (Fever, sepsis, dehydration)Altitude (Temperature PO2)Altitude (Temperature, PO2)SubmergedClothingClothingScavengers

EntomologyEntomology

Coleopterids (Beetles)

Major issues have to do withMajor issues have to do withCollection in the field and at autopsy

I di di-- Improper media or no media-- Failure to adequately document temperature

- on body- on body- beneath body - ambient

-- Humidity-- Environmental features

- antagonistic species (e.g. fire ants)- plant suppressors (e.g. cedar, certain forbs)

Certified professionals only-- Certified professionals only

1. Chlorosis2. Accelerated greening or browning3 Root activity3. Root activity

Plants

Mycota

Long Postmortem Interval(Months to years)

U ll i l k l t l ifi d i- Usually involves skeletal or mummified remains- Buried, submerged, scavenged- Wide range estimatesWide range estimates- Greater emphasis on environmental information

and concurrence methods- Varies widely by biotic province- Hampered heretofore by lack of understanding

f l hof long term changes

Adipocere formation

Mummification / Leatherization

“Wick” effectWick  effect

C ’ R lCasper’s Rule“One week open exposure = two weeks in waterOne week open exposure = two weeks in water = eight weeks buried”… Although hardly accurate summarizes the retarding effects ofaccurate, summarizes the retarding effects of burial and aquatic environments on decompositiondecomposition.

PMI in Skeletal MaterialChemical-- Staining (indophenol, Nile blue tetrazolium)-- Loss of total lipids-- Adipocere formation (saponification)-- UV fluorescence-- odor

Physical-- Specific gravity (density)-- Sound transmission -- UV Fluorescence-- C14 bomb curve data

Other-- Clothing fabric / associated artifact changes-- Concurrence (e.g. coins in pocket, environmental correlates)

R l i d i-- Relative dating

Rules you can live withy1. There is no single accurate marker of time of death aside from a

credible witness or a concurrence featurecredible witness or a concurrence feature.2. Accuracy declines as interval lengthens.3. Even with many variables accounted for, one should be cautious,

(W i t ddi t d t d t b t d ’t ft k h(We are a society addicted to data, but we don’t often know how independent variables interact)

4. A range should always be given. A report of a “specific” PMI is always suspect, and so is its author.

5. An opinion must not exceed a reasonable interpretation of the data or the methoddata or the method.

6. Beware of predispositional bias, (e.g. selection of methods or data that support one’s mind set.)

7 S l t t f ll7. Select experts carefully

S l t d R diSelected Readings

1. The Human Skeleton in Forensic Medicine, 2nd ed. W.M. Krogman and M. Yasar Iscaneds. C.C. Thomas Co., 1986 (Ch 2), ( )

2. Handbook of Forensic Pathology, 2nd ed. R.C. Froede ed. College of American Pathology, 2003 (Chs. 7 and 8)

3. The Estimation of the Time Since Death in the Early Postmortem Period, 2nd ed.C. Henssge, B. Knight, Thomas Krompecher, B. Madea, and L. Nokes, eds. Arnold Co.2002

4. Forensic Taphonomy: The Postmortem Fate of Human Remains W.D. Haglund andM. Sorg eds. CRC Press 1997