Stages of Decomposition: Effect of Time and Temperature

Stages of Decomposition Effect of Time and TemperatureChapter I INTRODUCTIONWatson, whoremonger you de boundaryine cause and while of wipeout? I knelt over the woman and began a cursory examination Rigor mortis has set in, so Id estimate shes been dead about 10 to 12 hours. Holmes stood up and napped himself off with his hands. So, that puts her demise between midnight and 2 am(Anonymous 2007).After the question of cause of cobblers last the question of period of final stage is the most sought after(prenominal) piece of information associated with a medical death investigation. As a consequence, death investigators find themselves in need of a means of ascertaining the period of clock between when an individuals body is found and when they died, sometimes referred to as the institutionalise mortem legal separation. Establishing the time of death through the determination of placement mortem interval may be set out a direct bearing on the legal questions of guilt or inno cence by confirming that a suspects alibi covers the period when the victim died, or demonstrating that it does not. If the time of death sess be established to within hours, days, months or even years, an individual may be able to prove that they were at some former(a) place at that time. On the other hand, if the suspect is known to have been in the vicinity of the victim during the appropriate time period, then they can be shown to have had an opportunity to commit the crime.Currently, on that point are denary techniques for determining post mortem interval that incorporate methods in almost every discipline of rhetorical science. Depending on the circumstances, these techniques can yield results that vary from a narrow accurate estimate (video of the victim, the victims stopped watch etc.) to a wide range estimate (counting guide rings on trees growing over or through the remains). Regardless of the of the method utilise, the calculation of post mortem interval is at best an estimate and should not be accepted as accurate without considering all of the factors that can potencyly move the result.Post Mortem Interval EstimationFor everything there is a season, And a time for every matter under heaven A time to be born, and a time to die Ecclesiastes 31-2The techniques currently utilized for estimating post mortem interval can be broken down into two broad categories base upon the methodology use. The first of these categories are the concurrence-based methodologies. Concurrence based methods relate or study the occurrence of a known event, which took place at a known time, with the occurrence of death, which took place at an unknown time. Examples of concurrence-based methods include the determining the years of comprise of clothing found on a body, tree ring breeding, dates on personal egresss, etc. Concurrence based methods rely on both recite associated with the body, and anamnestic evidence such(prenominal) as the de give the axeds normal pattern of movements. The second aggrouping of techniques include rate of change methodologies. Rate of change-based methodologies measure some manifestation of a evidence, directly associated with the body, that changes at a known or predictable rate and is started or stopped at the time of death. Examples of the rate of change based methods include body temperature, waver decomposition, insect epoch and tog out weathering. Some of these methodologies can be considered to fall into both categories. Examples of these would be tree ring development (Coyle, Lee et al. 2005) and insect succession.Previous post mortem interval Estimation MethodsThe florilegium of approaches for estimating post mortem interval spring from the varied expertise and experiences of their proponents as such the contrasting methods extend to be focused on the immediate needs of the investigator, and limited to a particular face of the post mortem interval or type of observation. As a consequence, the period of time for which a procedure is effective will overlap others.Algor, Rigor and Liver MortisTis after death that we measure men. James Barron holdThe earliest recorded methods for estimating early post mortem interval were a rate of change methodology based on the most intimately observed changes. The modify of the body after death (algor mortis), the gradual stiffening of the body (rigor mortis) and the fixed pooling of the blood resulting in discoloration of the lower portions of the body (livor mortis) can be easily surveyed with minimal or in some instances no instrumentation. Since the time of the ancient Greeks when the following rule of thumb was developedWarm and not stiff non dead more than three hoursWarm and stiff Dead between 3 and 8 hoursCold and stiff Dead between 8 and 36 hoursCold and not stiff Dead more than 36 hours (Starkeby 2004)until modern times, the basis of most temperature based post mortem interval analyses is the assumption that the human body, which averages 98.2 oF +/- 1.3 oF (Mall and Eisenmenger 2005), was at 98.6 oF (Mackowiak, Wasserman et al. 1992) at death and that after death the body looses heat in a predictable manner. on that point have been many temperature based methods for estimating post mortem interval. As early as the 1800s, Dr. John Davy had developed a method using the fall in body temperature (algor mortis), measured rectally, to determine the post mortem interval (Henssge and knight 2002). This method was refined by De Saram by recording detailed temperature measurements collected from executed prisoners (De Saram G. 1955). More recent approaches to this technique have included measuring rectal temperature, body surface temperature, ear canal temperature, eye socket temperature and liver temperature (Simonsen, Voigt et al. 1977 Henssge and Knight 1995 Baccino, De Saint Martin et al. 1996 Kane clutch, Kanawaku et al. 2006).Improvements to these techniques have included multiple progressive sampling, and the introduction of concepts such as the initial temperature plateau, core temperature, heat gradients, the effects of insulation, the ratio of surface area to volume, the effects of humidity and the effect of conductive surfaces, Microclimates and postmortem skin cooling (Green and Wright 1985 Nokes, rocky et al. 1992 Nelson 2000).However, most methods that attempt to use body temperature changes to determine the post mortem interval are hampered, as most methods are, by individual variability. Even when complex calculations and algorithms have been designed to model for tissue density, initial temperature distribution, post mortem exothermic reactions and heat loss, these refinements have not appreciably narrowed the estimate window for post mortem interval. denary studies outlining instances of initial temperature increase of a body soon after death (Hutchins 1985) associated with post mortem chemical changes such as rigor mortis, electric cell lysis and the conversion of c ellular energy production to anaerobic respiration (Nelson 2000) variations in the core body temperature ranging from 0.5 1.2 C during a 24 hour period (Chisholm 1911 Mackowiak, Wasserman et al. 1992) the effect of variable environmental temperatures (Green and Wright 1985 Green and Wright 1985) and the effect of environmental temperature on overall body surface temperatures (Mall, Hubig et al. 2002) have all contributed to limit the usefulness temperature as a consistent exponent of post mortem interval. Additionally, once the body has reached ambient temperature temperature ceases to be a factor. Marshall said it best when he said It would seem that the timing of death by means of temperature can never be more than an approximation(Henssge and Knight 1995).Soft and Hard Tissue DecompositionNow, a corpse, poor thing, is an untouchable and the process of decline is, of all pieces of bad manners, the vulgarest imaginable Aldous HuxleyCadaveric decomposition is a complex process th at begins immediately following death and proceeds beyond the time when recognisable human remains have ceased to exist. Decomposition can be broken down into two major stages. The first stage, soft-tissue decomposition, is caused by autolysis and putrefaction. Autolysis is the digestion of tissue by cellular enzymes and digestive processes normally present in the organism. Putrefaction is the digestion of whole tissues systems caused by the enzymatic use of fungi and bacteria that are all present in the organism or the environment that opportunistically invade the tissue. Both autolysis and the microorganisms responsible for putrefaction are normally held in check in living organisms. However, when an organism dies the cellular and systemic mechanisms responsible for regulating autolysis and inhibiting putrefying microorganisms stop. Without these controlling processes the body becomes fancy (bacterial) culture media (Carayannopoulos 1992). These early postmortem changes in soft tissues can be used to furnish an estimate of the post mortem interval from death until skeletonization. However, the rate of soft tissue decomposition can be dramatically affected by both internal and extraneous factors that affect the body (i.e. ambient temperature, cause of death, scavenging, trauma, environmental conditions, clothing, body size, mummification and adipocere formation) (Rodriguez and Bass 1985 Micozzi 1986 Mant 1987 Vass, Bass et al. 1992 Komar 1998 Campobasso, Di Vella et al. 2001). There are reported instances of rapid decomposition associated with acute illness (Frisch 2001) and the author is personally aware of an instance of a post mortem interval of less than 11 days resulting in complete skeletalization of an individual that died of complications related to Acquired Immunodeficiency Syndrome (Watson 1994). Additionally, there are a amount of examples of bodies remaining intact for years after death (Bass and Jefferson 2003).beyond gross observation for assessing decomposition, researchers have developed multiple morphometric and chemical methods for assessing soft tissue decomposition. These have ranged from early (ca.1800s) methods such as the Brouardel method which examined the shift in flammability of putrefaction gases in the early post-mortem interval, and the Westernhoffer-Rocha-Valverde method examining the formation of crystals in the blood formed after the third day of putrefaction (Cengage 2006) to more modern methods such as ultrasound assessments of organ condition (Uchigasaki, Oesterhelweg et al. 2004) and the use of electron microscopy to examine measurable physical changes in mitochondria (Munoz, de Almeida et al. 1999) and platelet count (Thomsen, Kaatsch et al. 1999). Chemical methods used to assess time since death include the assessment of volatile organic compound formation (Vass, Bass et al. 1992 Statheropoulos, Spiliopoulou et al. 2005 Statheropoulos, Agapiou et al. 2007 Dekeirsschieter, Verheggen et al. 2009 ) the concentrations of non-protein nitrogen (Sasaki, Tsunenari et al. 1983 Gallois-Montbrun, Barres et al. 1988) and creatinine (Gallois-Montbrun, Barres et al. 1988 Brion, Marc et al. 1991).Bony tissue decomposition, the second major stage of decomposition, consists of a combination of surface weathering due to environmental conditions (temperature, humidity, sunlight) and erosion from soil conditions (pH, mineral content, etc.) (Behrensmeyer 1978 Janjua and Rogers 2008). opus not much detailed study has been done on the environmental factors that affect bony tissue breakdown, it has been established that environmental factors such as pH, oxygenation, hydrology and soil flora and fauna can affect the long term stability of collagen (Garlick 1969 Henderson 1987 Bell, muleteer et al. 1996). Collagen, the primary protenatious component of bone, slowly hydrolyzes to peptides and then to amino acids leading to the breakdown of the collagen-mineral bonds which weakens the overall bone structure leaving it more vulnerable to environmental weathering (Henderson 1987). By examining the effects of related changes (cracking, flaking, vacuole formation, UV-fluorescence of compact bone) the investigator can estimate the period of time a bone sample has been exposed to weathering (Yoshino, Kimijima et al. 1991 Bell, Skinner et al. 1996 Janjua and Rogers 2008 Wieberg and Wescott 2008). Current methods of assessing time since death using bone weathering rely heavily upon the experience of the investigator (Knight and Lauder 1969) and are limited to immediately post skeletalization to 10 to 100 years based on environmental conditions (Haglund and Sorg 1997).As with the assessment of soft tissue decomposition for time since death, investigators examining bone decomposition have supplemented empirical methods with quantifiable testing techniques that analyze changes that are not directly affected by the physical environment (Lundquist 1963). Radiocarbon dating of carbon-14 and strontium-90 have been used to group remains pre and post 1950 (Taylor, Suchey et al. 1989 Maclaughlin-Black, Herd et al. 1992). Neis suggested that, with further study of strontium-90 distributions, determination of times since death should be possible (Neis, Hille et al. 1999). Bradley suggested that measuring the distribution of 210Pb and 210Po in marrow and calcified bone could prove forensically significant (Bradley 1993). This work was built upon by Swift who evaluated using 210Pb and 210Po distribution in conjunction with trace element compendium to provide a meaningful estimate of the post-mortem interval (Swift 1998 Swift, Lauder et al. 2001). Maclaughlin demonstrated that chemical changes due to environment could measurably affect isotope levels (Maclaughlin-Black, Herd et al. 1992). In addition to radionucleotide studies, investigators have besides measured the changes in both organic (amino acids, urea, proteins, deoxyribonucleic acid) and inorganic compounds (ni trogen, potassium, sulphur, phosphorous) in bone. (Jarvis 1997 Prieto-Castello, Hernandez del Rincon et al. 2007).Stomach Contents/Rate of DigestionGovern well thy appetite, lest sin surprise thee, and her black consecutive devastation. John MiltonThe presence or absence of food in the take over is often used as an indicant of post mortem interval. Its use as an indicator of post mortem interval is predicated on the assumption that under normal circumstances, the stomach digests and empties at a predictable rate taking from two to six hours to elapse a full meal (Jaffe 1989). If a person had eaten a light meal the stomach would empty in about 1.5-2 hours. For a medium-sized meal the stomach would be expected to take about three to four hours to empty. Finally, a large meal would take about four to six hours to exit the stomach. Regardless, it would take from six to eight hours for the initial portion of the meal to reach the large intestine (Hallcox 2007). This information, cou pled with reliable ante-mortem information relating to when an individual last ate is used by some pathologists when providing an estimate of the times since death. It is for this reason, among others, that comprehensive autopsies usually include an examination of the stomach contents (Batten 1995 Siegel 2006).Although it provides another useful indicator of time since death, there are serious limitations to the assessment of the stomach contents as an accurate indicator of time since death. Its reliance on reliable anamnestic evidence such as eating habits, the extent to which the victim chews their food (Pera, Bucca et al. 2002), the physiological state of the victim (Troncon, Bennett et al. 1994 Jayaram, Bowen et al. 1997 Lipp, Schnedl et al. 1997 Phillips, Salman et al. 1997) and the state of mind of the victim (Jaffe 1989) as well as verifiable antemortem evidence such as what the last meal consisted of (protein vs. fiber vs. fat)(Dubois 1985 Tomlin, Brown et al. 1993), the am ount of liquid consumed with the meal, alcohol consumption and the time when it was consumed limits its usefulness to a small number of cases (Jaffe 1989). These factors combined with evidence that digestion can bide after death (Koersve 1951) makes the estimation of post mortem interval using stomach contents concentrated at best.Insect SuccessionBuzzards gotta eat, same as worms. Clint Eastwood from the Outlaw Josey WalesInsect colonization of a body begins within hours of death and proceeds until remains cease to be a viable insect food source. Throughout this period, multiple waves of colonization by different insect species, as well as multiple generations of previously established species can exist. forensic entomologists can use the waves of succession and generation time to estimate the postmortem interval based on the variety and stage of development of the insects, or insect remnants, present on the body (Archer and Elgar 2003). In addition to information regarding time since death, forensic entomology can provide useful information about the conditions to which the body was exposed. Most insects have a preference for specific conditions and habitats when colonizing a body and laying their eggs. Modifications to that optimal habitat can interrupt the expected insect colonization and succession. The presence of insects or insect larva that would typically be found on bodies colonized indoors or in shade on a body discovered outside in direct sunlight may indicate that the body was moved after death (Sharanowski, Walker et al. 2008). Aquatic insects found on bodies discovered on land could indicate the body was originally in water (Wallace, Merritt et al. 2008 Proctor 2009).Although insect succession varies by season, geographical location and local environmental conditions, it is comm unless assumed to follow a predictable sequence within a defined habitat. While there are a multitude of studies that have examined regional succession patterns (Arche r and Elgar 2003 Tabor, Brewster et al. 2004 Tabor, Fell et al. 2005 Martinez, Duque et al. 2007 Eberhardt and Elliot 2008 Sharanowski, Walker et al. 2008) these studies use different approaches towards defining habitat and assessing insect succession making cross-comparisons of their info difficult. Also, the majority of these studies do not rigorously address the statistical predictability of a species occurrence making their results of limited use as post mortem interval indicators (Michaud and Moreau 2009). Additionally, beyond the presence or absence of clothing, the majority of the post mortem entomological studies conducted do not examine non-habitat external factors that may affect succession. For example, only a few studies have been conducted that assess the affect of drug ingestion (George, Archer et al. 2009) or the presence of chemicals (bleach, lye, acid etc.) used to cover-up evidence (Charabidze, Bourel et al. 2009) on the insect life cycle. As with other means of a ssessing time since death, more extensive studies with different insect species and drugs in a wider variety of habitats is necessary.Electrolyte ConcentrationDeath is a low chemical trick played on everybody J.J. FurnasCellular activity does not immediately cease when an organism dies. Rather, individual cells will continue to function at varying metabolic rates until the loss of oxygen and metabolic substrates caused by the cessation of blood flow results in hypoxia (low oxygen). As cell metabolism shifts from aerobic to anaerobic, oxidative phosphorylation and ATP generation, the cellular processes keeping autolysis in check, begin to decrease and eventually cease all together. Without energy to support osmotic gradients membranes begin to fail. As lysosomal membranes begin to fail the enzymes within are released and begin consuming the cell from the inside out. With autolysis comes a cascade of metabolic chemicals, released ions, originally bound up in various cellular process es begin to diffuse due to the diffusion gradient according to Ficks law into the intracellular spaces (Madea 2005). Forensic researchers have used the presence, absence or effects of inorganic ions such as potassium, phosphorous, calcium, sodium and chloride as a means of estimating time since death (Schleyer and Sellier 1958). In most instances the higher the concentration gradient, the more suitable is the analyte for the estimation of the time since death. When analyzing body fluids for the purposes estimating post mortem interval, early researchers tended to focus their studies on body fluids such as, cerebrospinal fluid, blood and pericardial fluid (Schleyer and Brehmer 1958 Coe 1972 Henssge and Knight 1995 Yadav, Deshpande et al. 2007) with a few others examining other compartmentalized bodily fluids (Madea, Kreuser et al. 2001) and the largest numbers focusing on vitrious humor (Madea, Henssge et al. 1989 Ferslew, Hagardorn et al. 1998 Madea and Rodig 2006 Kumagai, Nakayashi ki et al. 2007 Thierauf, Musshoff et al. 2009). Chemical methods used to assess these analytes in blood and spinal fluid as an indicator of post mortem interval have failed to gain general acceptance because, for the most part, they failed to create precise, reliable, and rapid results as required by the forensic community (Lundquist 1963). Current chemical methods which have primarily focused on vitreous fluid tend to suffer from the same limitations demonstrated by the fact that with notable exceptions (Pounder 1995) very few statistically rigorous field studies on the reliability and precision of estimating post mortem interval are available in the literature (Coe 1993 Madea 2005).Enzyme ActivityAs previously discussed, cellular activity does not cease when clinical death occurs. In any circumstances where the cellular metabolism shifts from a homeostatic balanced state to an imbalanced state biochemical changes occur. Changes in the levels and/or activity of enzymes (i.e. cardi ac troponin, c-reactive proteins, and G proteins) have long been used as indicators of cellular stress (Li, Greenwood et al. 1996 Katrukha, Bereznikova et al. 1998 Tsokos, Reichelt et al. 2001 Uhlin-Hansen 2001). Assessing similar changes in cellular biochemistry as a function of time since death provides investigators with a wide variety of tissues, testing methods and analytes for consideration. As a consequence, forensic investigators have assessed and suggested enzymes from heart, pancreas, muscle, blood and brain as potentially suitable markers for time since death (Wehner, Wehner et al. 1999 Wehner, Wehner et al. 2001 Kang, Kassam et al. 2003 Jia, Ekman et al. 2007 Poloz and ODay 2009). Comparisons of total proteins analyzed ante and post mortem analyzed using two dimensional gel electrophoresis and Matrix Assisted Laser Desorption/Ionization Time-of-Flight have demonstrated changes in metabolic enzymes, (Jia, Ekman et al. 2007 Hunsucker, Solomon et al. 2008). Assessing the ch anges in enzyme activity provides examiners a means to assess time since death, in many instances long before visible cellular changes. However, in at least a few of these studies results indicate that enzyme adulteration during extraction and partial enzyme activity observed with abasement products these markers better suited to soft analysis rather than quantitative analysis (Sabucedo and Furton 2003).Muscle/Nerve ExcitationBoth neurons and myocytes retain the ability to respond to electrical stimulation for at least a short period of time after organism death. (Sugioka, Sawai et al. 1995 Briskey, Kastenchmidt et al. 2002 Sams 2002). The resolution of flighty and muscle tissue to external electric stimulation has as well been investigated and proposed as means to estimate time since death (Kline and Bechtel 1990 Straton, Busuttil et al. 1992).Methods developed to investigate myocyte excitability assess the relative magnitude and duration of the muscle contraction during the application of external stimulation. To assess the contractile response, a combination of observational based assessments (Madea 1990 Jones, James et al. 1995) and measurement based assessments (Henssge, Lunkenheimer et al. 1984 Madea 1992) have been suggested and reported.Similar investigations have examined post mortem excitation of nervous tissue by measuring a variety of neurological reactions to stimuli. These include the alteration of Compound Muscle Action Potential (Nokes, Daniel et al. 1991 Elmas, Baslo et al. 2001 Elmas, Baslo et al. 2002), lengthen of the refractory or non-propagating period immediately following the CMAP (McDowall, Lenihan et al. 1998), the extracellular impedance/resistance (Querido 2000), the chronaxie measurement or the time over which a current double that necessary to enhance a contraction is applied before the contraction occurs (Straton, Busuttil et al. 1992) and the changes in the amplitude of the F-wave (the secondary CMAP observed after the i nitial CMAP) have all been examined, and been suggested as potential indicators of time since death.The results of studies examining the response of excitable tissue to electric stimulation have been consistent in that the stimulation response varies predictably over time. However, suitability for infrangible indicators of time since death remains in questions as investigators have reported contradictory results related to the effect of the manner of death on the stimulation response (Madea and Henssge 1990 Elmas, Baslo et al. 2002).RNA DegradationRNA degradation, both antemortem and postmortem, is a complex process that is not well understood. Unlike with desoxyribonucleic acid degradation, continuous degradation of inducible mRNAs by native ribonucleases is used as a means of translational control. After cell death these ribonucleases, no perennial kept in check by the mechanisms of cellular homeostasis, combine with exogenous ribonucleases from bacteria and fungi to begin un-in hibited digestion of all cellular RNA. Investigators have noted extensive variability in RNA degradation rates in different tissues (Bauer 2007). Not surprisingly such variability appears to be related to the antemortem ribonuclease activity of the tissue with relatively ribonuclease poor tissues such as brain and retina exhibiting greater RNA stability (Johnson, Morgan et al. 1986 Malik, Chen et al. 2003) when compared to ribonucleases rich tissues such as liver, stomach and pancreas (Humphreys-Beher, King et al. 1986 Finger, Mercer et al. 1987 Bauer, Gramlich et al. 2003). Additionally, but also not surprisingly, some constitutively expressed mRNAs have been shown to be more stable, or perhaps simply more prevalent, than inducible mRNAs (Inoue, Kimura et al. 2002). Additionally, while intrabrain mRNA levels are fairly constant, diencephalon levels vary considerably (Preece, Virley et al. 2003). As a consequence of these observations, the degradation of RNA (total and/or mRNA) hav e been suggested as a potential analyte to assess time since death.Researchers examining the effect of post mortem interval on RNA stability have examined a variety of targets (mRNA, both tissue specific and constitutively expressed, and total RNA) with an assortment of methods including Reverse transcriptase (RT) PCR(Ohshima and Sato 1998 Fleige, Walf et al. 2006 Haller, Kanakapalli et al. 2006 Zhao, Zhu et al. 2006), RNA (cDNA) microarrays (Bahn, Augood et al. 2001 Catts, Catts et al. 2005 Son, Bilke et al. 2005 Popova, Mennerich et al. 2008) and quantitative RT-qPCR (VanGuilder, Vrana et al. 2008). Based on these studies, there are indications that beyond time and temperature, factors such as hypoxia, tissue pH, antemortem physiological conditions (coma, seizure activity and injury) postmortem transcriptional activity and RNA sequence can dramatically affect the stability and measurable levels of RNA (Burke, OMalley et al. 1991 Harrison, Heath et al. 1995 Ohshima and Sato 1998 Ca tts, Catts et al. 2005 Bauer 2007). When examining the seminal question regarding time since death and temperature some researchers have reported temperature and time as significant factors affecting mRNA levels (Burke, OMalley et al. 1991), while others have reported the reverse (Harrison, Heath et al. 1995 Preece and Cairns 2003). These contradictory data are not surprising given the changes in the specificity, sensitivity and application of the assays used however, the ultimate question has not been resolved. What is clear from the research is that RNA degradation (mRNA or total) is a complex process (Preece and Cairns 2003 Preece, Virley et al. 2003 Heinrich, Lutz-Bonengel et al. 2007) effected by multiple factors indicating more study will be required before RNA degradation can be considered a reliable indicator of time since death.DNA Degradation and its Effect on DNA TypingSince the initial application of molecular(a) biology techniques to samples of forensic significance in the latter half of the 1980s, forensic scientists have noted that increased exposure to environmental insults can negatively impact DNA quality. Developmental validation studies performed to evaluate the efficacy of new typing techniques (SWGDAM 2008) have found that environmental variables such as heat, high humidity, direct moisture, fungous/bacterial contamination and ultraviolet light can impact the quantity or quality of the DNA sample making them unsuitable for DNA analysis (McNally, Shaler et al. 1989 Graw, Weisser et al. 2000 Takayama, Nakamura et al. 2003 Bender, Farfan et al. 2004 Schneider, Bender et al. 2004 Niemcunowicz-Janica, Pepinski et al. 2007). During transitions in technology from Restriction Fragment Length Polymorphism (RFLP) analysis to Polymerase Chain Reaction (PCR) based testing, researchers noted that samples too degraded to capture an RFLP pattern could still produce profiles using a variety of PCR based markers that evaluated loci shorter in length (Hoc hmeister, Budowle et al. 1991). This finding supports the hypothesis that degradation in the forensic background knowledge is (not surprisingly) processive. Additional research found that while the DNA in some samples like cadaveric blood and kidney tissue could degrade to the point where it was no longer suitable for DNA fingerprinting after as little as a week (Ludes, Pfitzinger et al. 1993) other samples such as bone (Hochmeister, Budowle et al. 1991 Frank and Llewellyn 1999) and teeth (Schwartz, Schwartz et al. 1991 Pfeiffer, Huhne et al. 1999) could, under most conditions, provide typeable DNA for months.The fact that DNA degradation has a detrimental effect on larger genetic loci, and affects different tissues at different rates is considered to be of extraordinary forensic significance is evidenced by the numbers of studies that seek to examine, and overcome this effect (42 validation studies specifically mentioning DNA degradation from 1995-2009 in PubMed). This makes perfe ct sense when the observer considers the impact that degradation can have on selecting suitable samples and evaluating the resultant DNA profiles. However, a number of researchers have looked beyond the simple question of how degradation affects the typing of samples to broader questions such as the mechanisms of postmortem degradation (De Mara and Arruti 2004 Foran 2006) and synthesis (Oehmichen, Frasunek et al. 1988) and how that knowledge can be used to assist in the assessment of time since death.DNA degradation by RFLPSince Sir Alec Jeffreys first applied Southern blotting (Southern 1975) techniques to the testing of forensically significant samples in 1985 (Jeffreys, Brookfield et al. 1985) DNA analysis has revolutionized forensic science. Restriction Fragment Length Polymorphism DNA analysis relies on variations in the lengths of DNA fragments generated by enzyme restriction. With restriction fragments ranging from virtually from 2 33 kilobases (Baird, Balazs et al. 1986) s uccessful typing and analysis requires high quality (un-fragmented) DNA. Researchers noted from the outset that in some cases involving older and/or postmortem samples that DNA degradation, tied to the exposures of higher temperatures, resulted in the gradual disappearance of the longer fragments reducing the evidentiary value of older samples (Bar, Kratz