Analysis of insect colonization and decomp materials in surrounding soil are two methods used to determine post mortem interval (PMI), and the interval during which a cadaver has been in a particular location. To note, neither is a perfect science, and variables apply.
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Forensic entomology is used most commonly to determine time since death. However, insects can provide other important information about a crime or victim. For example, insects can provide details about a person's life before they died. Because development is predictable depending on specific factors, the use of drugs can change the lifecycle timing of an insect.
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1. The presence of insects on the body that are not found in the area suggests the body was moved, and may indicate the type of area where the murder took place.
2. If the insect cycle is disturbed, it may suggest that the killer returned to the scene of the crime. The entomologist may be able to estimate the date of death and possibly the date of the return of the killer.
3. If maggot activity occurs away from a natural opening, this may indicate a wound. For example, maggots on the palm of the hands suggest defence wounds...
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LIMITATIONS OF FORENSIC ENTOMOLOGY:
1. Time of death estimates depend on accurate temperature information, but local weather patterns can be variable and data may come from stations quite distant from the crime scene.
2. Forensic entomology relies on insect abundance. In winter, there are fewer insects and entomology's use is limited.
3. Since it takes time to rear insects, forensic entomology cannot produce immediate results.
4. Treatments (like freezing, burial or wrapping) that exclude insects can affect estimates.
http://www.sfu.museum/forensics/eng/pg_media-media_pg/entomologie-entomology/
Soil chemistry under decomposing or dry remains of pigs and humans have been used to estimate post mortem interval (PMI) [2–4]
http://pawsoflife.org/Library/HRD/Aitkenhead_Peterson_2011.pdf
Typically, isotope analysis can prove to be particularly beneficial in establishing the likely age of remains. Isotopes are atoms of the same element, and with the same chemical properties, but differing in the number of neutrons within the nucleus (and thus have a slightly different atomic mass). Among the most common elements to be studied in isotope analysis are carbon, nitrogen, oxygen, strontium and hydrogen. This branch of study, which can be focussed upon unstable or stable isotopes, is based on the principle that many elements within the body exist as various isotopes, many of which are taken into the body by eating, for instance. Bones and teeth are usually subjected to isotopic analysis in cases of dating skeletonised human remains, though if present hair and nails may also be used.
http://aboutforensics.co.uk/forensic-anthropology/
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Understanding the life cycle of blow flies is extremely useful for murder investigations. Forensic entomologists, such as Watson, can determine approximately when insects found the corpse based on the blow flies' stage of development and the size of the maggots. This is different from estimating time of death, because multiple factors can influence the time of insect arrival. For example, a body could be stored in an airtight cooler for several days before being dumped in a field.
http://www.sciencedaily.com/releases/2011/11/111101125816.htm
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Soils—typically used by forensic science to link objects and persons with crime scenes—have since been shown to help locate clandestine graves1 and estimate time since death.2 This article will discuss soil characteristics for identifying the likelihood of a burial in soil, the breakdown of a cadaver in contact with soil, and the preservation of bone in soil. If soil morphological characteristics can help determine the likelihood of a burial and differential preservation, then it may be possible to make predictions prior to excavation using soil survey information.
http://www.forensicmag.com/articles/2012/02/soil-characteristics-impact-clandestine-graves