The Forensic Autopsy

The Forensic Autopsy 83

From: Forensic Science and Medicine: Criminal Poisoning, Second Edition By: J. H. Trestrail, III © Humana Press Inc., Totowa, NJ

83

Chapter 6

The Forensic Autopsy

“Revolted by the odious crime of homicide, the chemist’s aim is to perfect the means of establishing proof of poisoning so that the heinous crime will be brought to light and proved to the magistrate who must punish the crimi- nal.”—M. J. B. Orfila, 1817

6.1. T

A

During an autopsy, the forensic pathologist looks for certain clues that might indicate that a poison could have been involved in the death. These clues could include irritated tissues (from caustic and corrosive compounds);

characteristic odors, such as the almond-like odor of cyanide; or Aldrich- Mees lines (white bands on the nails that indicate chronic exposure to heavy metals such as arsenic) (see Fig. 6-1).

6.2. P

R

—“N

-K

”

The pathologist also reviews the results of any toxicological screens, to determine whether they are consistent with his or her pathological findings.

Certain cautions in the interpretation of the analytical toxicology results should be observed.

The concentrations of substances revealed by an analytical test will vary, depending on the site of origin of the specimen as well as the length of time that has passed since the initial exposure. The reliability of any postmortem specimen is directly related to the conditions associated with the collection of that specimen and the storage environment. It has become increasingly clear that the blood concentration of many drugs is definitely dependent on the site of collection, and that blood concentration may be significantly higher, or

84 Criminal Poisoning

sometimes lower, than at the time of death. If the pathologist removes blood merely from the left side of the heart or, worse yet, obtains a sample from the chest or abdominal cavity of the victim, this can yield results that may lead the investigator far astray from the actual meaningful and more accurate ana- lytical results. Unfortunately, the ability to interpret the results of toxicological analyses has not kept pace with the great advancements that have been made in the detection limits of analytical instrumentation.

It is unfortunate that the literature available on postmortem levels in fatal intoxications typically consists only of case reports. It would be of extreme value to forensic scientists if an international database listing chemical sub-

Figure 6-1

The Forensic Autopsy 85 stances that have been detected in bodies in relation to the time interval since death existed. This database should list the name of the substance, the type of specimen, the time interval since death that the specimen was obtained as well as analyzed, the determined level, and the type of analytical technique utilized. In other words, how long after death was it possible to prove the presence of a substance in the body? This information has major implications when considering the possible value of exhuming the body of a victim thought to have been poisoned.

It is well known that chemical substances redistribute in the body, a phenomenon often referred to as “anatomical site concentration” or “post- mortem redistribution.” This phenomenon could also well be called

“necrokinetics,” or the movement of substances after death has occurred.

Many studies have shown that the concentrations of certain drugs, such as propoxyphene and the tricyclic antidepressants, are increased in heart blood postmortem. Some researchers have proposed that drug concentrations obtained from liver specimens are much better indicators of toxicity (Hilberg, Rogde, & Morland, 1999; Jones & Pounder, 1987; Langford & Pounder, 1997).

Factors that can alter the movement of substances, and, therefore, their final concentrations in an analytical specimen, include acid-base changes in the body after death and the volume of distribution (Vd) of the substance in question. Volume of distribution is defined as that volume of fluid into which a drug appears to distribute to a concentration equal to that in plasma. Drugs with a low Vd will become less ionized as the pH (acidity) in the body decreases (i.e., becomes more acidic), and, therefore, their solubility in the surrounding tissues will increase. Examples of drugs that will shift with this change in acidity include salicylates, theophylline, and phenobarbital.

The ideal toxicological sample would be a peripheral sample obtained from a blood vessel that had been ligated shortly after death. Unfortunately, this ideal is seldom obtained in the case of homicidal poisoning.

6.3. A

G

The following guidelines must be kept in mind when carrying out a toxi- cological analysis:

• Postmortem concentrations are absolutely site dependent.

• Samples taken from the same site in the body will show different concentrations postmortem, depending on the time the sample was obtained.

• From a single postmortem measurement, no realistic calculation of the absorbed dose to create that level can really be made.

86 Criminal Poisoning

• When obtaining samples for analysis, a clean instrument must be used for each specimen, to avoid possible cross-contamination of specimens and erroneous re- sults.

• Both the death scene investigator and the pathologist can provide crucial infor- mation to the toxicological analyst.

• Absolute chain of custody must be maintained on all specimens throughout the process from their procurement through their toxicological analyses.

6.4. R

Hilberg T, Rogde S, Morland J: Postmortem drug redistribution—human cases related to results in experimental animals. J Forensic Sci 1999;44(1):3–9.

Jones GR, Pounder DJ: Site dependence of drug concentrations in postmortem blood—

a case study. J Anal Toxicol 1987;11:187–191.

Langford AM, Pounder DJ: Possible markers for postmortem drug redistribution. J Forensic Sci 1997;42(1):88–92.

Orfila MJB: A General System of Toxicology, or a Treatise in Poisons Found in the Mineral, Vegetable and Animal Kingdoms Considered in their Relations with Physi- ology, Pathology and Medical Jurisprudence. Carey & Son, Philadelphia, PA, 1817.

6.5. S

R

Druid H, Holmgren P: A compilation of fatal and control concentrations of drugs in postmortem femoral blood. J Forensic Sci 1997;42(1):79–87.

Imwinkelried EJ: Forensic science: toxicological procedures to identify poisons. Crim Law Bull 1994;30:172–179.

Moriya F, Hashimoto Y: Redistribution of basic drugs into cardiac blood from surround- ing tissues during early-states postmortem. J Forensic Sci 1999;44(1):10–16.

Pounder DJ, Jones GR: Postmortem drug redistribution—a toxicological nightmare.

Forensic Sci Int 1990;45:253–263.

Repetto MR, Repetto M: Habitual, toxic, and lethal concentrations of 103 drugs of abuse in humans. Clin Toxicol 1997;35(1):1–9.

Repetto MR, Repetto M: Therapeutic, toxic, and lethal concentrations in human fluids of 90 drugs affecting the cardiovascular and hematopoietic systems. Clin Toxicol 1997;35(4):345–351.

Repetto MR, Repetto M: Therapeutic, toxic and lethal concentrations of 73 drugs affect- ing respiratory system in human fluids. Clin Toxicol 1998;36(4):287–293.

Repetto MR, Repetto M: Concentrations in human fluids: 101 drugs affecting the diges- tive system and metabolism. Clin Toxicol 1999;37(1):1–8.

Watson WA: The toxicokinetics of poisoning and drug overdose. Am Assoc Clin Chem 1991;12(8):7–12.