C iConstructing (and Deconstructing)(and Deconstructing)

the Postmortem Intervalthe Postmortem Interval

H. Gill-King, Ph.D., D-ABFACenter for Human IdentificationCenter for Human Identification

Graduate School of Biomedical SciencesUniversity of North TexasUniversity of North Texas

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

General approaches

R h d / D h iRate methods / Death is a process, not an eventnot an event

Concurrence methods / One event fixed in time correlated with anotherfixed in time correlated with another

Sources of evidence

1 Corporeal / evidence from the1. Corporeal / evidence from the body

2 Environmental / contextual2. Environmental / contextual

3. Anamnestic / routines

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 required may vary considerably.

IntervalsIntervals

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

disruption of membrane pumps-- disruption of membrane pumps-- autolysis follows rate of glycolysis and

di d i Hcorrresponding drop in pH-- 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 state1. Agonal state-- hyperthermia / hypothermia

b li ( di b-- metabolic (e.g. diabetes, electrolyte imbalance, lacticy ,acidosis)dehydration-- dehydration

2. Body composition3. 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.

Algor mortis (cooling))g ( g))Dead bodies do not follow Newton’s ExponentialNewton s Exponential cooling curve for a variety of reasons.easo s.

Cooling variables

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

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

3 If outdoors extensive climatic changes which do not3. If outdoors, extensive climatic changes which do not allow for estimates of representative mean values.

4. General hypothermia or malignant hyperthermia.

i b li d h b d5. Remains believed to have been transported.

6. Body compositiony p

7. Clothing

8. Ambient temperature higher than 37C

9. Convection and humidity

10. Bodies are not uniformly dense. Core to shell andshell to environment transfer produces 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 hrs8-12 hrs. 4. Determined by body position for the first few

hours following deathhours following death

Quantitative measures of hypostasis, (colorimetric and hemoglobin concentration), correlate with PMI, but are not statistically validated Factors which affect quantification includestatistically validated.  Factors which affect  quantification include  1. Pigmentation2. Subcutaneous fat distribution / body composition3 A l t t3. Agonal temperature4. Ambient temperature

Other supravital methods

1. Chemical or neuromuscular induction -- iridial responsiveness to chemical stimulip-- electrical stimulation of mimetic and thenar muscles

2. Ocular changesl i-- corneal opacity

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

-- K+-- creatinine-- urea / glucose-- hypoxanthine / 3-methoxytyramine

Eye Changes1 “B i ” f ti l l ½ h1 “B i ” f ti l l ½ h1. “Boxcaring” of retinal vessels ½ hr

eyes > open closed1. “Boxcaring” of retinal vessels ½ hr

eyes > open closed2. Corneal film mins several hrs 3. Scleral discoloration mins several hrs2. Corneal film mins several hrs 3. Scleral discoloration mins several hrs3. Scleral discoloration mins several hrs4. Corneal cloudiness < 2 hrs 12-24 hrs5 C l it 3rd PM d

3. Scleral discoloration mins several 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

VariationsVariations- Liquid faster than semisolid faster than solid- Emotional state – psychogenic pylorospasm = delay- Emotional state psychogenic pylorospasm delay

for several hours- Hypermotility – 6-7 ft/hr…reaches cecum in 3 – 3.5Hypermotility 6 7 ft/hr…reaches cecum in 3 3.5

hrs (normal = 6-8 hrs)- CNS / spinal damagep g

mol/L

mmol/L

K+ [m

m

K+  [m

Intermediate postmortem intervalIntermediate postmortem interval(days to weeks)

- Supravital changes at endpoint- Greater emphasis on sceneGreater emphasis on scene - Increased reliance on structural changes

Expect wider time brackets- Expect wider time brackets- Changes are more subjective / less

ifi blquantifiable

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 withCollection in the field and at autopsy

-- Improper media or no mediaImproper media or no media-- Failure to adequately document temperature

- on bodyy- beneath body - ambientidi

“Garbage in,HumidityDrugs on board ?Environmental features

Garbage out” Environmental features

- Antagonistic species (e.g. fire ants)- Plant suppressors (e.g. cedar, certain forbs)pp ( g , )

Certified professionals only

Long Postmortem Interval(Months to years)(Months to years)

- Usually involves skeletal or mummified remainsUsually involves skeletal or mummified remains- Buried, submerged, scavenged- Wide range estimatesWide range estimates- Greater emphasis on environmental information

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

of long term changes- How much gravitas should we give theHow much gravitas should we give the

“body farms” ?

Pl t d M tPlants and Mycota

-- Leaf fall and seasonality-- Root activityy-- Charging effects-- Mold patchesMold patches-- Algal activity

Mycota

Adipocere formation

Mummification / Leatherization

“Wick” effect

PMI– Skeletal RemainsChemical Methods- StainingStaining- Loss of lipids- AdipocereAdipocere- CarbonatePhysical MethodsPhysical Methods- Specific gravity- Sound transmission- Sound transmission- UV fluorescence- Stable isotopes- Stable isotopes

OtherOther-- Clothing fabric / associated artifact changes-- Concurrence (e g coins in pocket environmentalConcurrence (e.g. coins in pocket, environmental

correlates)-- Relative dating (e g relation to construction)Relative dating (e.g. relation to construction)

C ’ R lCasper’s Rule“One week open exposure two weeks“One week open exposure = two weeksin water = eight weeks buried”…

Although hardly accurate summarizesAlthough hardly accurate, summarizes the retarding effects of burial and

i i d i iaquatic environments on decomposition.

Persistent Issues

1. When methods compete -- Do rate methods and corporeal evidence-- Do rate methods and corporeal evidence

trump concurrence and environmentaldata ?data ?

-- Is there a “hierarchy of methods” 2 Daubert challenges2. Daubert challenges

-- Many methods not validated on adequatesamples or under varied conditionssamples or under varied conditions

3. CSI effect-- Is it “sciency”enough ?-- Is it sciency enough ?-- Common sense vs. rocket science

Rules you can live withy

1. There is no single accurate marker of time of death aside from a credible witness or a reliable concurrence featurefrom a credible witness or a reliable concurrence feature.

2. Accuracy declines as interval lengthens.2. Accuracy declines as interval lengthens.

3. Even with many variables accounted for, one should be cautious, (We are a society addicted to data, but we don’t often know how variables interact)

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

5. An opinion must not exceed reasonableinterpretation of the data or the method.

6. Beware of predispositional bias, (e.g.selection of methods or data that s pportselection of methods or data that supportone’s mind set.

7. Attempt to achieve convergence using methodsbased on different premises. Wide discrepanciesrequire an explanation

8 S l t t f ll8. Select experts carefully.

9 Currently there is no unimpeachable way to determine9. Currently, there is no unimpeachable way to determine postmortem interval

“Pax ex jure etPax ex jure, etjus per scientiam”j p

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) Good summary of methods for the longer interval., ( ) y g

2. Handbook of Forensic Pathology, 2nd ed. R.C. Froede ed. College of American Pathology, 2003 (Chs. 7 and 8). Comprehensive but concise summaries of benchmark changes in bodies following death at various intervalschanges in bodies following death at various intervals

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 A good summary of various techniques, many experimental, for the short interval.Excellent bibliography. A useful guide to critiques of short interval estimates.

4 Forensic Taphonomy: The Postmortem Fate of Human Remains W D Haglund and4. Forensic Taphonomy: The Postmortem Fate of Human Remains W.D. Haglund andM. Sorg eds. CRC Press 1997 Good survey of the effects of various environments on rates of decomposition and skeletonization. Excellent bibliography.