Post-mortem interval

The post-mortem interval (PMI) is the time that has elapsed since an individual's death.[1] When the time of death is not known, the interval may be estimated, and so an approximate time of death established. Postmortem interval estimations can range from hours, to days or even years depending on the type of evidence present.[2] There are standard medical and scientific techniques supporting such an estimation.[3]

Stages of death
  1. Pallor mortis
  2. Algor mortis
  3. Rigor mortis
  4. Livor mortis
  5. Putrefaction
  6. Decomposition
  7. Skeletonization
  8. Fossilization
Timeline of postmortem changes.
Figure 1. Post-mortem phenomena to estimate the time of death.

Examination of body and scene of death

Changes to a body occurring after death (post-mortem changes) include:[3]

Conditions at the scene of death affect the estimation of time of death. To algor mortis, livor mortis and rigor mortis, together with consideration of stomach contents, there needs to be some observation of environmental conditions at the death scene to accurately measure the PMI (Fig. 1).[4] Factors that can effect the rate of human decomposition are concerned with the particular environment a body has been recovered from.[2] Bodies can be found anywhere from terrestrial to aquatic environments, each possessing their own variables that can alter interval estimations.[5] Along with common factors of temperature, humidity and element exposure, body habitus and clothing are an example of a component that can affect the rate of cooling of the body, and so its rate of decomposition.[5][6] A very approximate rule of thumb for estimating the postmortem interval is as follows:[7]

  • Warm and flaccid: less than 3 hours
  • Warm and stiff: 3 to 8 hours
  • Cold and stiff: 8 to 36 hours
  • Cold and flaccid: More than 36 hours.

Due to significant environmental variations between regions, universal formulas would be ill-suited for this topic in forensic science.[8]

Analytical techniques

There are analytical techniques that can be used to determine the post-mortem interval:[3]

  • Forensic entomology: insect (especially blowfly) activity on the corpse.[1]
  • Forensic botany: Plant and soil effects on the process of decomposition.[2]
  • Forensic pathology: Cause of death determination and subsequent postmortem changes[5]
  • Ocular changes: vitreous chemistry composition,[9] eye structural changes.[10]
  • State or stage of decomposition: autolysis (process of self-digestion) and putrefaction (process caused by bacteria found within the body).[11]

More advanced methods include DNA quantification,[12] infrared spectroscopy,[13] and for buried individuals changes in soil composition such as the levels of methane,[14] phosphates and nitrates,[15] ninhydrin-reactive nitrogen,[16] volatile organic compounds,[17] and water conductivity,[18] could also reveal the time of death.

References
  1. Jason H. Byrd; James L. Castner, eds. (2009). Forensic entomology: the utility of arthropods in legal investigations (2nd ed.). Boca Raton: Taylor & Francis. ISBN 978-0-8493-9215-3. OCLC 144565878.
  2. Pokines, James; Symes, Steven A., eds. (2013-10-08). Manual of Forensic Taphonomy. doi:10.1201/b15424. ISBN 9781439878439. S2CID 132436926.
  3. Simmons, Tal (2017-02-10), "Post-Mortem Interval Estimation: an Overview of Techniques", Taphonomy of Human Remains: Forensic Analysis of the Dead and the Depositional Environment, Chichester, UK: John Wiley & Sons, Ltd, pp. 134–142, doi:10.1002/9781118953358.ch10, ISBN 9781118953358
  4. Dix, Jay; Graham, Michael (7 December 1999). Time of Death, Decomposition and Identification: An Atlas. CRC Press. p. 1. ISBN 978-1-4200-4828-5.
  5. Sorg, Marcella; Haglund, William (2001-07-30), "Advancing Forensic Taphonomy: Purpose, Theory, and Process", Advances in Forensic Taphonomy, CRC Press, pp. 3–29, doi:10.1201/9781420058352-3, ISBN 978-0-8493-1189-5, retrieved 2022-04-14
  6. FBI Law Enforcement Bulletin. Federal Bureau of Investigation, U.S. Department of Justice. 1973. p. 12.
  7. Senior, T (2018). Forensic ecogenomics : the application of microbial ecology analyses in forensic contexts. London, United Kingdom San Diego, CA: Academic Press. ISBN 978-0-12-809360-3. OCLC 1023028365.
  8. Cockle, Diane L.; Bell, Lynne S. (2015-08-01). "Human decomposition and the reliability of a 'Universal' model for post mortem interval estimations". Forensic Science International. 253: 136.e1–136.e9. doi:10.1016/j.forsciint.2015.05.018. ISSN 0379-0738. PMID 26092190.
  9. Zilg, B.; Bernard, S.; Alkass, K.; Berg, S.; Druid, H. (17 July 2015). "A New Model for the Estimation of Time of Death from Vitreous Potassium Levels Corrected for Age and Temperature". Forensic Science International. 254: 158–166. doi:10.1016/j.forsciint.2015.07.020. hdl:10616/44849. PMID 26232848.
  10. De-Giorgio, Fabio; Grassi, Simone; d'Aloja, Ernesto; Pascali, Vincenzo L. (2021-05-01). "Post-mortem ocular changes and time since death: Scoping review and future perspective". Legal Medicine. 50: 101862. doi:10.1016/j.legalmed.2021.101862. ISSN 1344-6223. PMID 33610931. S2CID 231988953.
  11. Butzbach, Danielle M. (2010-03-01). "The influence of putrefaction and sample storage on post-mortem toxicology results". Forensic Science, Medicine, and Pathology. 6 (1): 35–45. doi:10.1007/s12024-009-9130-8. ISSN 1556-2891. PMID 19946767. S2CID 32152746.
  12. Lin, X; Yin, YS; Ji, Q (2011). "Progress on DNA Quantification in Estimation of Postmortem Interval". Fa Yi Xue Za Zhi. 27 (1): 47–9, 53. PMID 21542228.
  13. Huang, P; Tuo, Y; Wang, ZY (2010). "Review on Estimation of Postmortem Interval Using FTIR Spectroscopy". Fa Yi Xue Za Zhi. 26 (3): 198–201. PMID 20707280.
  14. Davla, M; Moore, TR; Kalacska, M; LeBlanc, G; Costopoulos, A (2015). "Nitrous Oxide, Methane and Carbon Dioxide Dynamics from Experimental Pig Graves". Forensic Science International. 247: 41–47. doi:10.1016/j.forsciint.2014.12.002. PMID 25544693.
  15. Senos Matias, MJ (2004). "An Investigation into the Use of Geophysical Methods in the Study of Aquifer Contamination by Graveyards". Near Surface Geophysics. 2 (3): 131–136. doi:10.3997/1873-0604.2004010.
  16. Van Belle, LE; Carter, DO; Forbes, SL (2009). "Measurement of Ninhydrin Reactive Nitrogen Influx into Gravesoil during Aboveground and Belowground Carcass (Sus domesticus) Decomposition". Forensic Science International. 193 (1–3): 37–41. doi:10.1016/j.forsciint.2009.08.016. PMID 19773138.
  17. Vass, A (2012). "Odor Mortis". Forensic Science International. 222 (1–3): 234–241. doi:10.1016/j.forsciint.2012.06.006. PMID 22727573.
  18. Pringle, JK; Cassella, JP; Jervis, JR; Williams, A; Cross, P; Cassidy, NJ (2015). "Soilwater Conductivity Analysis to Date and Locate Clandestine Graves of Homicide Victims" (PDF). Journal of Forensic Sciences. 60 (4): 1052–1061. doi:10.1111/1556-4029.12802. PMID 26190264. S2CID 12082791.
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