Реферат: Investigative Techniques To Determine Time Of Deat
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Investigative Techniques to Determine Time of DeathOne of the first steps involved in a homicide investigation is the determination of the time of death. While knowing the time of death is not crucial in each and every homicide case, it can be of significant importance in some. Except for a bullet passing through a victim’s head and striking a clock in the same room, determining time of death is not an exact science. However, there are a number of different indicators, most of which are evaluated during the autopsy, that can estimate the time of death to within hours. Accuracy will depend on such factors as the condition of the cadaver and its state of decay. Beginning at the crime scene, police officers can make a preliminary determination of the time of death by the body’s appearance and surroundings. Factors such as indicative acts, postmortem body temperature (algor mortis), postmortem lividity (livor mortis), stiffening of the body (rigor mortis) and putrefaction can all help to roughly estimate the time of death. Later, during the autopsy, forensic pathologists can examine more closely the above information as well as other factors such as stomach contents, chemical changes within the body, and insect activity, also known as “forensic entomology”. Starting at the crime scene, an investigator might look first at the indicative acts of the deceased. (O’Hara, 538)Indicative acts are those activities which the deceased may or may not have performed before death. If the victim is found in his or her home, non-medical evidence such as dates on uncollected newspapers, the condition of food in the house, or other customary acts not performed may give a relatively close estimate on time of death. In an outdoor crime, something such as the area underneath the body being unaffected by rain or snow could also set certain limits to the time lapse since death. (O’Hara, 540) However, probably the most reliable form of non-medical evidence are the statements of witnesses. (Hendrix, 19) If indicative acts or other non-medical evidence are not sufficient, then more scientific methods must be used, such as determining the postmortem temperature. Algor mortis, which means “the temperature of death” describes the cooling of the body. In ideal conditions, the rate at which a body cools is one degree per hour. However, factors such as the air temperature surrounding the corpse, body fat content, or immersion in water will cause the estimate to vary greatly. The following chart is based on a careful study of cadavers in a controlled environment with temperatures ranging from 59 to 68 degrees Fahrenheit:Rectal Temperature Time in Hours to Reachof the Cadaver the Indicated Rectal Temp. Minimum Maximum93 2 690 3 986 4 1282 6 1579 9 2075 12 2472 18 30This table shows that accuracy in pinpointing time of death decreases as the body’s core temperature decreases. Obviously, a span of 18 to 32 hours will be of little help to an investigator. (Wilber, 38). Fortunately, there are other methods to rely on, such as postmortem lividity. Livor mortis, which means literally “the color of death” is the discoloration of the skin caused by flow of blood into the venous spaces under the influence of gravity. Simply put, it is the blood pooling or settling into the lowest portions of the body. Livor is not considered to be a good indicator of postmortem interval, but there are some standards which can be seen. (Hendrix, 21). Anywhere from one-half to one hour after death livor can begin to be seen. Its appearance is similar to a bruise. In the early stages of lividity, (less than four hours) the skin, unlike a bruise, can be blanched when pressed. After four hours, the lividity has begun to set, and by six to ten hours, it has reached its maximum and is permanent. (Wilber, 39) Postmortem lividity is caused by the red blood cells settling into the veins and capillaries in the lowest portions of the body which causes a red color to appear in the skin beneath. Later, the red cells will break down and squeeze out of the capillaries into the body, thus making the lividity permanent. Therefore, livor is commonly used by investigators to determine whether or not a body has been moved after death. (Baden, 37) Because lividity, as stated earlier, is not a good indicator of postmortem interval, investigators may also look to another sign of death, rigor mortis. Rigor is a more common indicator of postmortem interval. Under normal environmental conditions, the muscles of a cadaver will stiffen (not contract) with a set pattern and rate. This is caused by dead muscle production of lactic acid fusing with the myocin in the muscles and forming a gel. This gel causes the stiffness. (Starkeby, Internet 1) The smaller, shorter muscle groups of the face and neck are affected first, and the stiffness gradually works its way down the body to the legs. Rigor can begin to set in fifteen minutes after death or fifteen hours after. The average time is five to six hours. (O’Hara, 539) Different temperatures can cause variations in the rate that the body stiffens. Heat will cause rigor to set in quicker, whereas cold will slow the process; therefore, these factors must be considered when making a determination of the time of death. (Wilber, 27) In temperate regions, the following rule of thumb can be used in estimating death, but it must be used with caution:If the body feels:Warm and not stiff: Not 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 hoursNotice that after approximately 36 hours, the effects of rigor mortis will disappear. Rigor mortis should never be the only basis for estimating time of death. (Starkeby, Internet 1)An interesting case which relied upon an accurate time of death estimate for a conviction was the John Belushi drug overdose case in Los Angeles. Belushi had been on a four day drug binge with a Canadian friend and drug groupie Cathy Smith. Smith was the last person to see Belushi alive, and she also administered his last injection of heroin. Discrepancies between the time she gave Belushi his last injections and the medical examiner’s time of death estimate led to her charge and conviction of involuntary manslaughter. According to Smith, she gave Belushi his last injection on March 5, 1982 at 3:30 a.m. The injection was a “speedball”, a mixture of cocaine and heroin. Later she stated that heard Belushi coughing and brought him a glass of water at 7:45 a.m. He went to sleep, and at 10:15 a.m. she left him alive and sleeping and went to a bar to bet on a horse. At 12.30 p.m., Belushi was found dead by an exercise instructor. Emergency Medical Services (EMS) arrived at 12:35 p.m. and Smith returned at 1:45 p.m. Pressure was put on the Los Angeles District Attorney by Belushi’s wife to prosecute Smith because she sold a story of Belushi’s last hours to the National Enquirer. When police came to question Smith, she fled to Canada. Giving someone drugs is not an extraditable offense in Canada, but murder is; therefore, the Los Angeles DA needed very persuasive evidence that Smith had caused Belushi’s death. The medical examiner first needed to determine the time of death. According to EMS, Belushi was found with stiffness around the jaw, which is where rigor begins. EMS had stated that they had trouble placing an airway in his mouth. This early stage of rigor would have taken an hour or two to set in, making the time of death between 10:30 a.m. and 11:30 a.m. However, rigor couldn’t be relied on alone, because it sets in more rapidly on someone who is very active before death. So the examiner looked at lividity. The coroner had examined Belushi and taken pictures of him at 4:37 p.m. The pictures show a definite purplish color on his back, which corresponds to how he was found, and the skin blanched when pressed. This state of lividity is right for about six to eight hours after death, thus putting time of death between 8:30 a.m. and 10:30 a.m., earlier than rigor would indicate. The coroner also took Belushi’s postmortem temperature at 4:37 p.m. It was 95 degrees F. Using the standard rule of thumb, which is the body cools after death one degree per hour, this would put the time of death around 1:00 p.m., half an hour after the exercise instructor found him dead. Obviously something was wrong. The EMS had already confirmed at 12:35 p.m. that rigor mortis had started. There were a couple of reasons for the temperature to be off. Belushi was overweight, and the amount of fat around the organs can affect the rate of temperature loss. Also, heavy cocaine use will cause the muscles to shiver and quiver, thus raising the body temperature. Belushi’s temperature could have been as high as 100 degrees F at the time he died. Even so, he could not have died before 10:30 a.m. That many hours would have caused his temperature to be below 95 degrees, regardless of the aforementioned circumstances. All the information taken from rigor, livor and algor mortis pointed to a time of death between 8:30 a.m. and 1:00 p.m. Rigor put death between 10:30 a.m. and 11:30 a.m. Livor put it at 8:30 a.m. to 10:30 a.m., but rigor ruled out the earlier time, as did algor. Death at 8:30 a.m. was too early for Belushi’s temperature to be as high as 95 degrees F by 4:37 p.m. Thus, time of death was figured to be at 10:30 a.m., give or take an hour.
What ultimately led to Cathy Smith’s conviction was the determination that Belushi died of a heroin overdose and not from cocaine. Belushi had twice the lethal level of morphine in his bloodstream. Morphine is the breakdown chemical of heroin, which consists of a combination of morphine and acetic acid. Belushi had enough heroin in his system to kill two people. Given that amount, he would have died within two hours of the injection. If the 3:30 a.m. speedball injection was the final one, Belushi should have been dead by 5:30 a.m. Yet Smith said he was alive and talking at 7:45 a.m. By her own word, she was still with Belushi at 8:30 a.m., she didn’t leave for the bar until 10:30 a.m. When the police were finally able to question Smith, she changed some of the times. She told police that Belushi had taken a shower around 6:30 a.m. (not after the 3:30 a.m. injection) and that she gave him a glass of water at 9:30 a.m. (not at 7:45 a.m.). This story confirmed that the 3:30 a.m. injection was not the last one. People with twice the lethal amount of heroin in their systems do not walk, talk, drink water and take showers. Smith never admitted to giving Belushi an injection after 3:30 a.m., but the medical evidence was against her. She consequently served fifteen months in jail for involuntary manslaughter. (Baden, 84 – 90). Reflecting back for a moment to indicative acts, if the approximate time of the victim’s last meal can be determined, a medical examiner may be able to conclude time of death by examining the body’s stomach contents. In order for this method to be as accurate as possible, the investigator should also determine the size of the meal and what specific foods were eaten. This will give the medical examiner a good starting point for making his determination. He will look at both the position of the food in the stomach and its degree of digestion. All digestion processes cease at the time of death. Armed with the information given above, a pathologist can judge time of death by looking at how far the food in the stomach has moved. Food begins to empty from the stomach and into the intestines ten minutes after eating a meal. Light meals may take up to two hours to empty from the stomach, whereas a large meal may require up to six hours. The pathologist will compare the location of the food to the information about the victim’s last meal to make his estimation. In order to confirm his estimation, the pathologist can also look at the degree of digestion. Digestion is the physical and chemical breakdown of food. There are several factors which will cause the rate of digestion to vary from person to person, but the primary rate depends on how long the food has been in the stomach and intestines. The medical examiner can use this to make a rough determination of the time since the victim’s last meal and his death. (O’Hara, 541)Many other chemical changes occur within the body after death that can be drawn upon for determining time of death. The sum of these changes is called putrefaction, which is due to the action of bacteria on dead tissue. The major source is saprophytic bacteria in the gastrointestinal system that spread throughout the body. Time of death indicators abound in putrefaction, but they are all extremely variable due mainly to temperature. Along with putrefaction, there are other tissue changes, such as autolysis, which can serve as good time of death indicators, but like putrefaction, they are also variable with temperature Autolysis is an enzymatic destruction of tissues which begins at death. Pathologists can read the interval of autolysis to make time of death estimates. (Hendrix, 21) There have been cases where a homicide victim’s body was found unusually well preserved. Since the time constraints for algor, rigor and livor mortis have long since past, chemical changes must be relied upon. Such was the case in the 1977 Pinchos Jaroslawicz murder investigation in New York City. Pinchos Jaroslawicz was murdered and his body was placed in a plastic bag and hidden in a basement. The temperature in the basement never rose above forty degrees F. Bacteria do not thrive in a cold environment, so there was no putrefaction after more than a week. Obviously after being dead this long, time of death could not be pinpointed to the hour; however, the pathologist in this case used what was at the time a new technique of determining time of death called the potassium eye fluid test. The test measures the level of potassium in the eye fluid. In life, there is a small amount; however, after death the red cells break down and the potassium in them enters the vitreous fluid at a predictable rate. The major advantage to this test is that it is unaffected by temperature. Using the potassium eye test, the pathologist in the Jaroslawicz case was able to accurately confirm time of death as eight days from when the body was autopsied. (Baden, 96) If the body is beyond putrefaction and chemical changes, there is still one more method to look at to estimate time of death, forensic entomology. It is common knowledge that death attracts insects. What is not common knowledge is that there are scientists called forensic entomologists who specialize in estimating time of death. They do so by estimating what stage of life the insects that inhabit the body are in. Entomologists know which insects are generally the first to arrive, and at what stages of decomposition that other insects will begin to arrive. The insects that usually arrive first are the Diptera, commonly called “blowflies” and Sarcophagidae, or “fleshflies”. In temperate regions, they will usually arrive within fifteen minutes of death. The female blowflies will lay their eggs on the body, especially around the natural orifices. Eggs will also be laid in any open wounds. Fleshflies do not lay eggs, but will deposit larvae. Little change happens to the blowfly egg in the first eight hours, and total egg stage will typically last about a day. Once hatched, the larvae grow at a predictable rate. The larval stages of development are called instars. Blowfly larvae have three instars. The first instar is approximately five millimeters long after 1.8 days. The second instar is approximately ten millimeters long after 2.5 days, and the third instar is approximately 17 millimeters long after 4 to 5 days. A more precise way forensic entomologists use to determine age of larvae and eggs is called “rearing”. The entomologist raise a test group of blowflies for comparison to those found at the crime scene. For example, a body is found with masses of blowfly eggs on it, none of which have hatched. How long has it been since the eggs were deposited (oviposited)? The entomologist will note the time of discovery and then note the time when the first instar larvae occur. He will subtract the time of the first larvae hatch from the time of the body’s discovery and call that time “A”. He will then rear those flies to adulthood, breed them on raw beef liver under conditions similar to the crime scene and measure the time from oviposition to the hatching of the first instar larvae and call that time “B”. By subtracting “B” from “A”, he will get “C”, which is an estimation of the time since oviposition on the body until its discovery. This is just an one example many ways forensic entomologists can estimate time of death. The succession of various organisms on cadavers happens in a fairly predictable sequence. As stated earlier, blowflies and fleshflies arrive first, and as putrefaction develops, more groups arrive at the scene, with most groups present just before the body dries out due to seepage of liquids. There are other insects which will show up after the body has dried out, which can provide fairly accurate time of death estimates three to six months back, possibly even further. (Starkeby, Internet 2)In conclusion, determining time of death is never an exact science, but with sound investigative techniques and a lot of help from science, the estimate can be pretty close. When a body has been discovered, investigators should start by first looking for indicative acts surrounding the body and questioning witnesses. This may be all that is needed to determine time of death, if it even needs to be known. Time of death could be just a footnote on a death certificate, or a crucial part of a prosecutor’s case. In any event, investigators should be aware of the tools and the science that is dedicated to the accurate measurement of postmortem interval.
Baden, Michael M., M.D., and Hennessee, Judith Adler Unnatural Death. New York: Random House, 1989Hendrix, Robert C., M.D. Investigation of Violent and Sudden Death, A Manual For Medical Examiners. Springfield, Illinois: Charles C. Thomas, 1972O’Hara, Charles E. And O’Hara, Gregory L. Fundamentals of Criminal Investigation, Sixth Edition. Springfield, Illinois: Charles C. Thomas, 1994Starkeby, Morten (Internet 1) What happens after death?Web Site: www.uio.no:80/ mostarke/forens_ent/afterdeath.htmlStarkeby, Morten (Internet 2) Forensic Entomology and Estimating Time of Death. Web Site: www.uio.no:80/ mostarke/forens_ent/forensic_entomol_pmi.htmlWilber, Charles G, Ph.D. Forensic Biology for the Law Enforcement Officer. Springfield, Illinois: Charles C. Thomas, 1974Back to Lebo’s Term Paper PageBack to Lebo’s Home PageE-Mail mehttp://pages.prodigy.com/termpapers