Effect of Burning on Minimum Post-Mortem Interval (Minpmi) Estimation from an Entomological Perspective

Effect of Burning on Minimum Post-Mortem Interval (Minpmi) Estimation from an Entomological Perspective

AEFS 1.1 (2017) 17–31 Archaeological and Environmental Forensic Science ISSN (print) 2052-3378 https://doi.org.10.1558/aefs.32472 Archaeological and Environmental Forensic Science ISSN (online) 2052-3386 Effect of Burning on Minimum Post-Mortem Interval (minPMI) Estimation from an Entomological Perspective Amoret P. Whitaker University of Winchester and Natural History Museum, London [email protected]; [email protected] Forensic entomologists are often employed to estimate the minimum post-mortem interval of bodies in cases of untimely or unexplained death. Although some cases have involved burnt remains, few studies have been carried out to assess whether ento- mology can still be utilised. Only one major study has been carried out which deter- mined that even after a major house fire, blow fly larvae can still be identified and used to estimate a minimum post-mortem interval. Most studies have investigated whether burning affects the attraction of blow flies to burnt bodies, and their subsequent ovi- position. Results vary, but suggest that blow flies may be more likely to oviposit on bodies which have undergone considerable burning, where the splitting of the skin has resulted in the exposure of suitable oviposition sites, whereas bodies only mildly burnt may be too dry for oviposition. In addition, although most studies have utilised some type of accelerant to facilitate the burning, this has not been taken into account with regards to blow fly attraction or larval development. This review paper gives an overview of the current literature relating to burnt bodies and the use of entomology to estimate a minimum post-mortem interval in such cases. Forensic entomology is the study of insects within a legal context, and can be divided broadly into three main areas of interest—stored product pests, urban entomology, and, the area in which the term is most frequently applied, medico-legal cases (Hall et al. 2012). In the latter area, a forensic entomologist may be employed to assist a legal investigation in cases of myaisis (the infestation of live animals or humans by insects) or in cases of unexplained or untimely death, most often to estimate the minimum post-mortem interval (minPMI) (Hart et al., 2008). Although it is one role of forensic pathologists to estimate time since death, the methods they employ, including the post-death conditions of livor mortis, algor mortis and rigor mortis, are only really applicable during the first 48–72 hours after 18 Amoret P. Whitaker death (Campobasso et al. 2001) and even then there is considerable variation (Bourel et al. 2003). Beyond that time, the pathologist uses their medical knowledge and experience to estimate time since death. In some cases, the body may have died or decomposed under particular conditions which may affect the normal decomposi- tion process. These conditions may include anaerobic environments, where the body has been hidden or otherwise enclosed, and thus decomposed in an oxygen-starved environment. Factors such as clothing, and the type of materials involved, may also affect decomposition processes (Goff 1992). Burial (Payne et al. 1968) and underwater (Payne and King 1972) environments will also alter the usual decomposition process, and fire will alter the body by causing dehydration and reduced protein content (Campobasso et al. 2001). In order to estimate the minimum post-mortem interval, the forensic entomologist estimates the age of the insects colonising the body. In the majority of cases, the first insects to do this are the blow flies (Diptera: Calliphoridae). Both males and females detect a body by the odour it omits during the early stages of decomposition (Cam- pobasso et al. 2001), but females are attracted in much larger numbers. The males feed on the body and take advantage of the mating opportunities, and the female also feeds on the body and lays her eggs (oviposits) on it. The eggs hatch out into 1st instar larvae, which feed on the body’s soft tissues, and moult into two further stages, 2nd and 3rd instar. Once they have completed their feeding stage of development, the larvae generally disperse away from the body to find a suitable pupariation site, although some species such as Protophormia terraenovae pupariate on the body itself (Busvine 1980). The age of the insects is calculated using a method based on pre-determined rates of development, which differ between even closely related species. Insects are poikilothermic, with their rate of development depending on the external temper- ature, thus the colder it is the slower they develop, and the hotter it is the faster they develop (Ames and Turner, 2003). Therefore forensic entomologists can esti- mate an insect’s age (i.e. the time they were laid as eggs [sometimes as larvae] on the body) using a method of ADD (accumulated degree days) or ADH (accumulated degree hours), which is calculated by time x days or time x hours, respectively. Thus, if you know the number of ADD/ADH required for a species to reach a certain stage of development, and you can estimate the temperature at which it was developing, you can estimate the time taken for the insect to reach that stage. However, it is impor- tant to emphasise that it is the minimum post-mortem interval that is being esti- mated, i.e. the time since egg-laying, rather than actual time since death. Although blow flies have an extraordinary sense of smell, and may locate a body within min- utes of death, the time taken for the female blow fly to locate and lay her eggs on the body, sometimes referred to as the pre-oviposition period (POP), is uncertain. Under some circumstances egg-laying may be considerably delayed, such as if the body is wrapped, buried, enclosed, submerged in water, indoors, or somehow less accessible to the blow fly (Goff 1992; Mann et al. 1990). One condition which may affect the pathologist’s estimation of time since death is that of a burnt body, caused by fire and resulting in physical changes to the body. In © Equinox Publishing Ltd. 2017 Effect of Burning on Minimum Post-Mortem Interval 19 CGS Level Description Level # 1 Constitutes burn injuries characteristic of typical smoke death. The body may exhibit blistering of the epidermis and singeing of the head and facial hair. Recovery of the body is similar to that for other victims not involving burn injury. The body is recognizable for identification at this level. Level # 2 Defines a body that may be recognizable but most often exhibiting varying degrees of charring. Further destruction of the body is limited to the absence of elements of the hands and/or feet, and possibly, the genitalia and ears. Addi- tional searching near the body is warranted for recovery of disarticulated ele- ments. Identification is made, most often, by the collaboration of medical exam- iner and forensic odontologist. Level # 3 Shows further destruction of the body, with major portions of the arms and/or legs missing. The head is present at this level although identity is non-recognis- able. The search area for associated disarticulated remains should be widened. A forensic anthropologist should be included to facilitate successful search and recovery procedures at the death scene. Identification is co-ordinated by a medical examiner who may require the aid of a forensic odontologist. If needed, a forensic anthropologist may be called on to determine gender, age, race, etc. from the skeleton. Level # 4 Corresponds to a degree of extensive burn destruction whereby the skull has fragmented and is absent from the body. Some portions of the arms and/or legs may still remain articulated to the charred body. Search and recovery should be aided by a forensic anthropologist using systematic bioarchaeological methods including screening procedures to locate small body fragments and dental elements. Identification is coordinated by a medical examiner using forensic anthropologist and odontologist consultants, as needed. Level # 5 Represents the final level of the proposed scale. At this level, the body has been cremated and little or no tissue is present. The remains are highly fragmentary, scattered and incomplete. A forensic anthropologist should be an on-site con- sultant for identification and recovery of the cremains. Personal identification is most difficult at this level and a forensic anthropologist may be best trained to interpret cremains for identifying physical attributes of the deceased. Recovery of dental elements will require the expertise of a forensic odontologist. As with all fire deaths, a medical examiner is, mostly likely, the designate to coordinate consultant activities. Table 1. Crow-Glassman Scale (CGS) for describing the extent of burn injury to human remains (Glassman and Crow 1996). a retrospective study carried out in France (Fanton et al. 2006) on the causes of fires involved in the deaths of 40 people, it was found that 52% of the fires were accidental, 16% were caused as part of a suicidal act, and 31% were a criminal act. In the latter case, the most likely reason was in order to cover up a homicide by attempting to destroy evidence. As a result of the recovery of ~80 bodies at the Branch Davidian compound at Mount Carmel in Waco, Texas, in 1993, and the subsequent investigation, it was recognised that although there existed an accepted and recognized scale of burn injuries for living subjects, based on the “degree” of burns, i.e. percentage, depth and extent of damage (Glassman and Crow 1996), there was at that time no such universal scale to describe © Equinox Publishing Ltd. 2017 20 Amoret P. Whitaker the extent of burn damage to deceased bodies. Glassman and Crow (1996) therefore produced the Crow-Glassman Scale (CGS) which is divided into five levels, with each succeeding level describing increasing destruction of the body, outlined in Table 1.

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