Informacion

Chapter 5
Estimating time since death
With the discovery of human remains, one of the most important issues to be considered postmortem interval, that is, the amount of time that has elapsed since the death of the decedent. As described in Chapter 1, this is one of the statistics used to examine missing persons files in search of a likely match. Therefore, its accurate determination may makethe difference between identifying the deceased or a body that remains unclaimed.
In the first hours after death, medical investigators use a variety of methods to estimate postmortem interval. These include livor mortis (settling of blood in the body),algor mortis (cooling of body temperature after death) rigor mortis (muscle stiffness), and changes in vitreous humor (changes in the fluids of theeye). However, after only 24 hours these methods become less accurate so that, by the time soft tissue has begun to decompose, they are unusable. It is at this point that the techniques used by forensic anthropologist and other specialists are employed to estimate this statistic.
After death, a number of organisms and other agents begin to break down the body, causing a general loss of skin,internal organs, and other body components. These organisms include large animals that will remove and consume much of the soft tissue. In addition, bacteria will break down internal organs, causing putrefaction. Similarly, plants will grow on, under, and between body segments, while physical factor (e.g., weather) will break up, bury transport, and otherwise damage the remains. Studies of the rate atwhich these agents work have led forensic specialists in several disciplines to determine timetables for various.
One such specialty is forensic taphonomy. While taphonomy is the branch of science that deals with changes to biological organisms between the time of death and the time of discovery, forensic taphonomists study the stages through which the human body passes from being “fresh” tobeing completely skeletonization. In addition, they study the schedule by which animals eat, disarticulate, and otherwise modify biological remains. Thus postmortem interval is estimated by knowing the amount of time needed for bodies to reach stages of deterioration, given a particular climate and the amount of accessibility to small and large animals.
In addition to taphonomy, other fields havecontributed significantly to estimating time since death. The broad area of entomology (the study of insects) includes forensic entomology, which is the study of insect life cycle and succession on cadavers for the purpose of the determining postmortem interval. Similarly, forensic scientists within botany (forensic botany) use plant growth as a method of estimating this interval. Also variousother specialists study the amount of deterioration of clothing, paper money, and other such items to yield estimates of time since death. Finally, a variety of other more complex techniques (e.g. chemical analysis of soils near bodies, amount of degeneration of DNA) can be employed when the proper equipment and personnel are available.
This chapter will present four topics concerning thedetermination of time since death. First, the process of decomposition will be described, with an emphasis on the agents that cause the human body to break down and the factors that affect the rate with these agents work. The second section presents the schedules by which decompositional changes occur in different geographical areas of North America and under different conditions of body deposition (e.g.,surface, burial, submersion).The third section deals with timetables for determining postmortem interval from animal scavenging, including soft tissue consumption, scattering of skeletal elements, and gnawing of bones. The last section discusses methods used by specialists in other fields; these are included here because forensic anthropologists may need to collect and preserve elements used by...