C Constructing i (and Deconstructing) (and Deconstructing) the Postmortem Interval the Postmortem Interval H. Gill-King, Ph.D., D-ABFA Center for Human Identification Center for Human Identification Graduate School of Biomedical Sciences University of North Texas University of North Texas
E stimation of the postmortem interval E stimation of the postmortem interval remains a persistent challenge, and one of the most important in forensic science. 1 1. Inclusion and exclusion of suspects Inclusion and exclusion of suspects 2. Civil applications 3 3. Establishing medicolegal significance Establishing medicolegal significance
General approaches R Rate methods / Death is a process, h d / D h i not an event not an event Concurrence methods / One event fixed in time correlated with another fixed in time correlated with another
Sources of evidence 1 1. Corporeal / evidence from the Corporeal / evidence from the body 2 2. Environmental / contextual Environmental / contextual 3. Anamnestic / routines
Progression of events Progression 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, although the dwell time in each stage and the l h h h d ll i i h d h overall time required may vary considerably.
Intervals Intervals Short interval (hours to days) -- irreversible circulatory arrest irreversible circulatory arrest -- global ischemia -- disruption of membrane pumps disruption of membrane pumps -- autolysis follows rate of glycolysis and corrresponding drop in pH di d i H -- observable changes
Short interval contd. Rigor mortis – Generalized stiffening of the Rigor mortis Generalized stiffening of the Muscles / onset 2-4 hrs, resolution 24-84 hrs.
Onset and duration will be affected by 1 Agonal state 1. Agonal state -- hyperthermia / hypothermia -- metabolic (e.g. diabetes, b li ( di b electrolyte imbalance, lactic y , acidosis) -- dehydration dehydration 2. Body composition 3. Ambient conditions at the scene
A dditional problems A dditional problems 1 S bjecti it in staging 1. Subjectivity in staging 2. Lack of contextual information from the scene Use of rigor mortis as the sole indicator of Use of rigor mortis as the sole indicator of PMI should be avoided.
Algor mortis (cooling)) g ( g)) Dead bodies do not follow Newton’s Exponential Newton s Exponential cooling curve for a variety of reasons. easo s.
Cooling variables 1. Strong radiation (e.g. solar or proximity to a heating or cooling device) 2. Uncertain alternating temperatures (e.g. HVAC system, windows open, etc.) i d t ) 3 If outdoors extensive climatic changes which do not 3. 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. i b li d h b d
6. Body composition y p 7. Clothing 8. Ambient temperature higher than 37C 9. Convection and humidity 10. Bodies are not uniformly dense. Core to shell and shell to environment transfer produces a plateau with significant resulting variations during the first 6 hrs.
Livor mortis (hypostasis ) 1. Visible soon after death. 2 Easily ‘blanched’ for a few hours 2. Easily blanched for a few hours. 3. Usually ‘fixed’ and cannot be blanched within 8 12 hrs 8-12 hrs. 4. Determined by body position for the first few hours following death hours following death
Quantitative measures of hypostasis, (colorimetric and hemoglobin concentration), correlate with PMI, but are not statistically validated Factors which affect quantification include statistically validated. Factors which affect quantification include 1. Pigmentation 2. Subcutaneous fat distribution / body composition 3 A 3. Agonal temperature l t t 4. Ambient temperature
Other supravital methods 1. Chemical or neuromuscular induction -- iridial responsiveness to chemical stimuli p -- electrical stimulation of mimetic and thenar muscles 2. Ocular changes -- corneal opacity l i -- segmentation (“boxcaring”) of retinal vessels 3 Transit time of gastric contents 3. Transit time of gastric contents 4. Vitreous analytes -- K+ -- creatinine -- urea / glucose -- hypoxanthine / 3-methoxytyramine
Eye Changes 1. “Boxcaring” of retinal vessels ½ hr 1 “B 1. “Boxcaring” of retinal vessels ½ hr 1 “B i i ” f ” f ti ti l l l l ½ h ½ h eyes > open eyes > open closed closed 2. Corneal film mins 2. Corneal film mins several hrs several hrs 3. Scleral discoloration mins 3. Scleral discoloration mins 3. Scleral discoloration 3. Scleral discoloration mins mins several hrs several hrs several hrs several hrs 4. Corneal cloudiness < 2 hrs 12-24 hrs 4. Corneal cloudiness < 2 hrs 12-24 hrs 5. Corneal opacity 3 rd PM day 5. Corneal opacity 3 rd PM day 3 rd PM d 3 rd PM d 5 C 5 C l l it it
Food in Stomach Variations Variations - 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 – 3.5 Hypermotility 6 7 ft/hr…reaches cecum in 3 3.5 hrs (normal = 6-8 hrs) - CNS / spinal damage p g
K+ [m mmol/L K+ [mm mol/L
Intermediate postmortem interval Intermediate postmortem interval (days to weeks) - Supravital changes at endpoint - Greater emphasis on scene Greater emphasis on scene - Increased reliance on structural changes - Expect wider time brackets Expect wider time brackets - Changes are more subjective / less quantifiable ifi bl
Decompositional / Putrefactive changes Slippage – Breakdown at intercellular junctions Separation at papillary line Marbling - Heme degradation + H 2 S Ferrous sulfide Bulla(e) – Capillary fluid / plasma between skin layers Bloating – Enteric anaerobes and facultatives ramp up fermentative rate. Increased rate of hydrolysis of protein, lipid, carbohydrate substrates Purge fluid – Autolysis of upper GI and respiratory tracts P fl id A t l i f GI d i t t t
Slippage Bullae Bullae Marbling Bl Bloating ti Purge fluid
I t Interpretation subject to: t ti bj t t Ambient temperature (Q 10 rule) Ambient temperature (Q 10 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 PO 2 ) Altitude (Temperature, PO 2 ) Submerged Clothing Clothing Scavengers
Entomology Entomology
Coleopterids (Beetles)
Major issues have to do with Collection in the field and at autopsy -- Improper media or no media Improper media or no media -- Failure to adequately document temperature - on body - beneath body “Garbage in, - ambient Humidity idi Garbage out” Drugs on board ? Environmental features 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 remains Usually involves skeletal or mummified remains - Buried, submerged, scavenged - Wide range estimates Wide range estimates - Greater emphasis on environmental information and concurrence methods and concurrence methods - Varies widely by biotic province - Hampered heretofore by lack of understanding Hampered heretofore by lack of understanding of long term changes - How much gravitas should we give the How much gravitas should we give the “body farms” ?
Pl Plants and Mycota t d M t -- Leaf fall and seasonality -- Root activity -- Charging effects -- Mold patches Mold patches -- Algal activity
Mycota
Adipocere formation
Mummification / Leatherization “Wick” effect
PMI– Skeletal Remains Chemical Methods - Staining Staining - Loss of lipids - Adipocere Adipocere - Carbonate Physical Methods Physical Methods - Specific gravity - - Sound transmission Sound transmission - UV fluorescence - - Stable isotopes Stable isotopes
Other Other -- Clothing fabric / associated artifact changes -- Concurrence (e g coins in pocket environmental Concurrence (e.g. coins in pocket, environmental correlates) -- Relative dating (e g relation to construction) Relative dating (e.g. relation to construction)
C Casper’s Rule ’ R l “One week open exposure “One week open exposure = two weeks two weeks in water = eight weeks buried”… Although hardly accurate summarizes Although hardly accurate, summarizes the retarding effects of burial and aquatic environments on decomposition. i i d i i
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