Introduction
It is now over 70 years since Locard laid down the first principle of crime scene management, ‘every contact leaves a trace’. With recent advances in fingerprint retrieval, footwear impression enhancement by electrostatic methods, and the ability to recover DNA from even a single cell, the avoidance of contamination has achieved prime importance. Indeed, cross-contamination, real or alleged, is often of more use to the defense team than is the loss of an occasional fiber or hair – although the importance of trace evidence preservation cannot be too strongly emphasized.
In many jurisdictions, crime scene management has become an increasingly specialized area of police practice. Courses and diplomas are offered in the subject and the scenes of crime officer (SOCO) now assumes many responsibilities that were at one time shared by the pathologists, forensic scientists and other crime scene specialists. However, this is not the case in every country; there are situations where the pathologist may be the only trained professional at the scene. Furthermore, the pathologist’s specialist knowledge and advice are frequently sought, especially when the locus, or the nature of materials of potential evidential value are somewhat unusual. It should also be borne in mind that a senior pathologist with a heavy case load may well have been attending scenes and performing autopsies when the most senior police officer involved was still at school, and the pathologist will certainly attend more scenes every year than the average junior detective. Pathologists, therefore, cannot devolve responsibility on to others. Their errors of omission or commission may well be exposed in court, devaluing their testimony as a whole.
The pathologist’s involvement in evidence preservation
The pathologist should assume responsibility in the following areas:
• selection of appropriate samples;
• proper collection of samples;
• avoidance of loss of material;
• avoidance of cross-contamination;
• selection of appropriate containers and preservatives;
• appropriate packaging;
• assurance of health and safety;
• labeling and storage;
• maintenance of continuity;
• proper disposal of contaminated material and ‘sharps’;
• advice to the court on production of material in court (for example, blood-stained clothing).
These considerations apply at the scene, in the mortuary and subsequently in all areas of the laboratory investigation.
Preservation of Evidence at the Scene (‘The Locus’)
On arrival at the scene the pathologist should introduce himself to the senior investigating officer (SIO) and to the SOCO. Before entering the building or the cordoned-off area, a plan of action and division of responsibility should be agreed upon.
The designated approach route should be identified and rigidly adhered to. Is the pathologist to be responsible for ‘taping’ clothing and exposed areas of skin, or will a scientist/SOCO fulfill this role? To whom will the pathologist hand each sample, and who will assume responsibility for its recording and labeling? How many persons will actually approach the body closely? Forward planning is essential; the one thing one should not do at a crime scene is ‘make it up as you go along’!
Appropriate full protective clothing should be worn. This should comprise overalls, rubber boots or overshoes, gloves and head covering. This author regards facemasks as an ineffective nuisance; they provide little protection against infection or odor, they are uncomfortable, and people tend to fiddle with them – a dangerous practice in these days of single cell DNA. Overalls without pockets are to be preferred; this avoids the temptation to take sweet wrappers, soiled tissues and other sources of contamination to and from the scene. The pathologist can always persuade the exhibits officer or SOCO to hold a clipboard and pen. It should be remembered that the handheld tape recorder has no place in these circumstances, certainly not in UK jurisdictions. The only records of evidence acceptable in UK courts are contemporaneous notes made at the time. Furthermore, tape recorders are unreliable. They are subject to damage by dropping or bad weather. If it is decided to use a tape, it can be used for no other purpose thereafter. It must be retained in perpetuity and certified copies must be made available to the defense.
The body should be photographed in situ, and a diagram drawn. It should then be decided what trace evidence and samples to collect at the scene, and what may safely be left until the body has arrived in the mortuary. Climate may well influence these decisions; a threatened downpour or a howling gale are both good reasons for choosing expedient removal.
Tapings from exposed skin and clothing should be taken. This author prefers low impact fingerprint lifting tape, but ordinary Scotch tape serves just as well. However, it is much more likely to adhere to gloved fingers. Each ‘lift’ is then pressed down upon a clear acetate sheet and appropriately labeled. Any suspicious stains on skin or clothing should be lightly swabbed with a cotton-wool bud, moistened with tap water, before the lift takes place. A control water-moistened swab should also be retained and submitted for examination. Blood spots may have originated from the victim or the assailant(s). Several should be sampled.
If clothing or other material, weapons, etc. need to be lifted from the body, their position should be recorded photographically; they should then be individually labeled and bagged. Wet and soiled clothing should be taken in brown paper bags to an appropriate drying area before packeting and onward transmission to the forensic science laboratory.
Taking mouth and pharyngeal swabs before the body is disturbed prevents contamination by reflux of stomach contents, bronchial secretions or continuing oozing of blood from facial injuries. Semen may also occasionally be found in gastric contents (see below).
Swabs from the female genital organs and from the anus pose more of a problem. There are arguments for taking these at the mortuary rather than at the scene, particularly if conditions are cramped and the lighting is poor. On the contrary, there is always the risk of drainage of vaginal secretions on to the peri-anal area during transport, leading to incorrect assumptions of anal sex; the same problem may arise if the rectal temperature is taken before the swabs are collected. It has been successfully argued in court that semen found deep in the rectum was transferred there by the clumsy insertion of a thermometer probe; this can be avoided by collecting the high vaginal, introital and anal swabs before inserting the rectal probe or thermometer.
In cases where a sexual motive may be suspected, and the breasts or buttocks are exposed, it is wise to take swabs from the nipples and surrounding skin, the buttocks, the suprapubic area and the front of the neck, even if there are no stains visible to the naked eye. Saliva traces may be found, even if no bitemarks or suction bruises are visible. The perpetrator may have masturbated over the victim rather than having full intercourse. Those forced to commit fellatio may spit out the seminal fluid so that it is found on the clothing or even on the ground nearby.
The recording of the distribution of blood spatter and staining, and the collection of representative samples there from, is usually the responsibility of the SOCO or the forensic scientist. Even so, the pathologist should take some note of its presence and distribution. It may well relate to the pattern of injuries which is subsequently found. The pathologist should also remember that the body is only a part of the scene; the trained eye may spot a stain or fragment of tissue in an area of disturbance, or appreciate the significance of a discarded tablet or a foil wrapper which has been missed by the lay observer.
The body should then be prepared for transportation to the mortuary. Bags should be placed over the head, hands and feet. They should be loosely secured, preferably with adhesive tape. String or twine, too tightly applied, can create factitious ‘ligature marks’ and lead to confusion. Plastic bags are most commonly used, although some police forces in the United Kingdom are switching over to brown paper, which gives rise to less condensation and moisture artifacts. If the body lies at a fire scene, nylon bags prevent the evaporation of accelerants. The body should then be carefully lifted on to a polythene sheet. The ready-made zipper body bag is not always suitable. Most of them provide barely enough room for a body of average build which lies in the anatomical position and is free of rigor mortis; bodies with established rigor or those fixed in the pugilistic attitude following exposure to heat may not fit within the limited space. Even worse, the zippers have a habit of sticking, or breaking open during transit.
It is the pathologist’s responsibility to supervise the lifting and the removal of the body. Rough handling, especially in elderly osteoporotic subjects, may produce fractures, particularly of the cervical spine and the necks of the femurs. Clumsy bumping of the body against walls, pieces of furniture or other projections can produce skin lesions that may occasionally cause confusion, although such postmortem abrasions are usually readily distinguished from injuries sustained during life. Strict instructions should be given that the body and its coverings must remain undisturbed until the pathologist’s arrival at the mortuary. Ideally, the body and the sheeting should be left in the shell or casket so that its removal can also be supervised. Unfortunately, the funeral director or other body removal contractor may be reluctant to allow this; it may be needed urgently for another case.
Finally, the site where the body lay should be minutely examined for further trace evidence. The area should be photographed again. Before leaving the scene, the pathologist should check all the exhibits collected, ensuring that the record tallies with that of the police. He or she should sign the appropriate labels, give advice on the storage of perishable materials, such as tissue fluids and swabs, and issue appropriate warnings on health and safety (see below).
Examination at the Mortuary
The pathologist’s responsibilities for preservation of evidence continue throughout the autopsy and its aftermath. Occasionally it may become necessary to collect further samples, particularly for toxicology or DNA profiling, at a later date. As at the scene, the pathologist should work as a member of the team, and adhere to a previously agreed protocol, which may be modified appropriately in special circumstances.
Samples and exhibits are collected for three principal reasons. Firstly, to establish the identity of the deceased if this cannot be determined by conventional means. Secondly, to demonstrate any form of contact,including sexual, between the deceased and the per-petrator(s), and, finally, to establish the cause of death, or the presence of any extraneous factors that might have contributed to it, for example microscopic evidence of natural disease, or the presence of alcohol, drugs or other toxic substances.
External examination
All those present in the autopsy suite should wear full protective clothing and gloves from the outset. Only the SIO, SOCO and photographer should be ‘about the body’; other spectators should be confined to a designated viewing area.
Clothing and connected property
The pathologist should assume responsibility for lifting of the body on to the autopsy table, the removal of the protective plastic wrappings and bags, and an initial close scrutiny of the clothing in situ. Each exhibit should be bagged separately and labeled appropriately.
Careful examination of the clothing may reveal the presence of hitherto unnoticed stains, fibers, dirt and other materials. It is also important to record the presence and direction of bloodstains and splashes before they have been obscured by the removal of the clothing. These may provide information as to the position of the assailant during the assault, and any movement of the body thereafter.
Each item of clothing should be removed intact, the pockets searched, and then bagged (wet clothing should be allowed to dry out first). Sometimes a suicide note may be found in the pocket, leading to the immediate solution of the ‘crime’. Remember that drug abusers may have unsheathed used needles wrapped in a handkerchief or tissue, so proceed with caution. In infants, the presence of blood-stained mucous stains about the mouth, on the clothing or on the bedding, is particularly significant. Natural sudden infant death may be associated with slightly pink respiratory secretions. Frankly blood-stained material should raise the possibility of mechanical asphyxia, particularly if exudation continues hours after death.
In cases of stabbing, the clothing damage should be matched to the injuries on the body. Suicides, for example, tend to lift or open the clothing first and then stab the exposed area. In some shootings, a spent bullet or fragment thereof may lie in the folds of the garments, and can be readily lost if care is not taken. Furthermore, in any case of shooting, the hands and clothing should be swabbed for firearms residues before undressing is undertaken. Different police forces use different techniques and reagents for this, and so local protocol should be followed.
If any form of penetrating injury (not just gunshot wound) is present, radiographic examination should be considered. The broken tip of a knife blade or the fragment of some other weapon may be located; so might drug-laden condoms or other containers in the intestines or body orifices. A full skeletal survey is mandatory in any case of suspected physical child abuse. The limbs, head and trunk should be individually X-rayed in all the appropriate planes by a competent radiographer. The so-called ‘two plate babygram’ does not reveal adequate detail of subtle bony injury, such as hairline fractures of long bone shafts or ‘slipped epiphyses’.
The collection of ‘intimate samples’ should now be undertaken. A generous handful of plucked head hair, roots and all, should be collected. Hair should also be collected, with roots, from the eyebrows, pubic region, beard and moustache. Use disposable forceps or the gloved hand. Nail scrapings should be taken with a cocktail stick, or the nails clipped with freshly cleaned scissors. These may be used for DNA profiling. The sample is also of use to the toxicologist searching for poisoning by agents such as arsenic or thallium, and for evidence of use of drugs of abuse over a period of time. Swabs from the mouth, anus, vagina and penis should be collected. Plain swabs are used. They should be stored frozen. Blood substance grouping is no longer used routinely in England and Wales; in those jurisdictions where these techniques are still in use, samples (again on plain swabs) should be stored at 4-8°C. It is wise to take a large number of swabs (at least three), particularly from the vagina and the anus. This ensures that even small amounts of material are recovered. Some pathologists and forensic scientists use unwaxed dental floss for recovery of traces of semen from between the teeth.
Swabs should be taken from any suspicious stains elsewhere on the body. Special attention should be paid to any matted or crusted pubic hairs. The axillary hair should also be examined; semen may, albeit uncommonly, be recovered from the armpits. A comb may be used to recover material from crusted areas of hair.
Any dust, grit or earth soiling of the body should be sampled, either by taping or swabbing. Some police forces are attempting to recover fingerprints and footwear impressions from skin and from clothing. It would appear that these attempts have so far met with little success in the UK. The FBI are experimenting with ultraviolet lighting. Other methods, such as iodine fuming, have been abandoned.
If the body is colonized by insect pupae or maggots, these should be recovered and preserved in an alcohol-glycerol mixture; formaldehyde is not suitable.
Internal examination
Blood and urine should be recovered under direct vision, rather than by blind probing through intact skin. Uncontaminated urine, for both toxicology and microbiology, is best obtained with a needle and syringe through the dome of the bladder. If the bladder is almost empty, it may be opened and a few milliliters recovered from its base with a syringe devoid of needle.
The choice of site of blood samples for toxicology remains controversial. More than 20 years ago it was shown that there were wide variations in barbiturate levels, depending upon sample sites. More recently, other workers have confirmed these observations using other drugs. Furthermore, they have demonstrated that diffusion of drugs from the stomach may give artificially high levels in blood from the heart or the venae cavae. It has been well known for many years that samples taken from these sites are unreliable owing to contamination from the liver, where concentrations are frequently much higher than they are in peripheral blood. Cavity blood should never be collected for any purpose; it is certain to be contaminated with intestinal organisms. The ideal sites for blood collection are the femoral or common iliac vein. Ideally, separate samples should be taken from each side, and the lower of the two values obtained should be regarded as being most acceptable for court purposes. If the abdomen is heavily contaminated, small amounts of blood can be recovered from the femoral or popliteal vessels.
Ocular vitreous humour is the fluid of choice for biochemical tests such as electrolyte, urea and glucose levels. It may also be used for toxicology in mutilated bodies, those that have been exposed to extreme heat, or are undergoing early putrefactive change. The vitreous should not be taken at the start of the autopsy in any child where head injury might be even a remote possibility. Its extraction renders the eyes useless for histological examination. Only after the scalp, skull and brain have been examined should vitreous humour be taken in these circumstances. In child deaths, cerebrospinal fluid should be taken at the commencement of the autopsy by direct vision from the cervical canal, using a pipette, after the vertebral arches have been removed. This fluid can be used for microbiology, toxicology and biochemistry.
If poisoning is suspected, samples of liver and brain should be taken and frozen in separate containers. Most modern toxicology laboratories can carry out a full range of tests on as little as 20 g of these organs. The stomach contents should be collected; the forensic scientists may wish to determine the composition of the last meal (and sometimes look for the presence of semen) before passing them on to the toxicologists. Only rarely is it necessary to retain the contents of the small bowel. Few toxicology laboratories now require the stomach itself, but in cases of poisoning by such materials as arsenic, the advice of the tox-icologist should be sought before the postmortem is concluded. The pathologist should routinely take tissue samples from all major organs for microscopy. An autopsy without full histology is regarded by truly professional pathologists as incomplete. It is certainly not acceptable in the modern court process, be it civil or criminal.
Preservation of Samples
Many toxicology laboratories are happy to accept unadulterated urine, provided it has been refrigerated and delivered in a reasonable time (24-36 h). A few still prefer the addition of a preservative such as a small amount of phenyl mercuric nitrate.
Blood is more of a problem. Samples for DNA profiling should have no preservative added, but should be frozen. It is now generally agreed that measurement of blood alcohol levels is unreliable if commercial fluoride/oxalate containers are used. These are perfectly adequate for fresh venous samples from living patients which are to be analyzed within a very short time. Postmortem samples are liable to production of alcohol by microbiological action, and higher concentrations of sodium fluoride are required to inhibit this. Forensic science laboratories now recommend the addition of sodium fluoride to a concentration of at least 1% weight for volume, i.e. a generous ‘knifepoint’ of the crystals to a 5 ml sample bottle. ‘Vacutainers’ or similar prepacked ven-epuncture appliances are not suitable for use at autopsy. They work well for venesection in the living, but they are difficult to use when extracting blood from the cut end of an iliac vein. A plain syringe – or even an accurately placed (and clean) dessertspoon -is to be preferred.
Solid organs and stomach contents should be frozen. Vitreous humor and urine should be refrigerated at 4-8°C. Samples for microbiology are liable to yield fallacious and misleading results. Even with prior ‘searing’ of the surface of the organ, for example the heart or lung, with a hot scalpel blade, postmortem contamination is almost inevitable. In the vast majority of cases, a simple nutrient blood culture bottle, and plain swabs rather than those coated with or immersed in transport medium, should be used. It should be made clear to the receiving microbiology laboratory that these samples are from postmortem material. The microbiologist who issues the report should then be able to interpret more accurately the significance of any organisms that are grown.
The pathologist’s final responsibility is to check the exhibits log, sign all the labels, and ensure that all the specimens are secure from leaks and that appropriate advice on storage is given and is clearly understood. The risks of virus infections, notably Human immunodeficiency virus (HIV) and blood borne hepatitis, are now higher than formerly. In any case where the deceased may have had a suspect lifestyle (for example, sexual promiscuity or intravenous drug abuse), consideration should be given to appropriate screening of a blood sample.
