Forensic History – Locard’s exchange principle

Dr. Edmond Locard (1877–1966) was a pioneer in forensic science who became known as the Sherlock Homes of France where he was the director of the very first crime laboratory in existence, located in Lyon.  He formulated the basic principle of forensic science: “Every contact leaves a trace”.  This became known as Locard’s exchange principle.

Essentially Locard’s principle is applied to crime scenes in which the perpetrator(s) of a crime comes into contact with the scene, so the perpetrator(s) will both bring something into the scene and leave with something from the scene.  Every contact leaves a trace.

“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him.  Not only his fingerprints or his footprints, but his hair, the fibres from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects.  All of these and more, bear mute witness against him.  This is evidence that does not forget.  It is not confused by the excitement of the moment.  It is not absent because human witnesses are.  It is factual evidence.  Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent.  Only human failure to find it, study and understand I, can diminish its value.”

The objective of forensic evidence is to prove or exclude a physical connection between individuals and objects or places.  Such evidence comprises a wide variety of substances or objects, the analysis of which requires specific, often specialised scientific skills.

The close encounter of perpetrator, patient and crime scene may result in an interchange of traces of evidence (Locard’s principle).  Biological traces (i.e. hair, blood, semen, skin fragments) may be found on both the patient and perpetrator; for instance, the perpetrator’s blood could get onto the patient’s clothing.

On the basis of the facts available and information provided by the patient and investigators, the healthcare practitioner must decide which samples to collect from the individuals involved.  When faced with such decisions, it is important to be mindful of what purpose the sample will serve, what link is potentially going to be established and whether such a link may assist the investigation of the case.

Important points to keep in mind when conducting an examination of a victim of sexual violence (the patient) with a view to obtaining forensic evidence are:

• Consent is required.  Information gained under informed consent may need to be provided to other parties, in particular, law enforcement authorities (i.e. the police) and the criminal justice system if the patient pursues legal action on the case.  Also see OBTAINING CONSENT, page xx.
• It takes time to conduct a thorough forensic examination; the examination usually involves a “top-to-toe” inspection of the skin and an ano-genital examination.
• Detailed documentation is required; information so recorded may be used in criminal proceedings.
• Certain areas of the body (e.g. the axilla, behind the ears, in the mouth, the soles of feet) not usually examined as part of a routine medical examination are of forensic interest and must be inspected.
• Unusual evidence, such as clothing, drop sheets and hair, are collected as part of a forensic examination.
• The chain of custody of evidence must be documented.  Also see Preserving The Integrity Of Evidence
• Opportunities for follow-up examinations may not arise; it is thus vital to make full use of this single patient contact.  Collect the maximum amount of relevant evidence.

There is a wide range of samples that could be collected in order to assist the criminal investigation process.  It is essential that healthcare practitioners have a clear understanding of the capabilities and requirements of the Forensic Science Laboratory.  The available evidence collection kits will lead the healthcare practitioner through the process.

The Patient As A Crime Scene

Few other criminal offences require as extensive an examination and collection of evidence as a sexual assault.  Apart from an occasional assault case, no other crime collects as much evidence from a living person.

While a potentially fatal object (bullet, knife, etc.) may be removed from someone and taken to the forensic laboratory for analysis, that person is not required to submit to the same intrusive examination as a patient of sexual assault.  So, it is not unreasonable to assume that having your person subjected to scrutiny, your blood and hair samples taken, your fingernails scraped and every orifice that has already been violated swabbed with polyester on a stick can be a devastating experience.  This User Guide Manual is designed to make the collection of evidence from a human being as thorough, timely, and humane as we have the knowledge and capacity to do.

The body of the patient could possibly contain many physical clues.  Your contribution is a key success factor in ensuring that the forensic evidence is correctly collected that can in turn ultimately lead to the prosecution of the perpetrator or the exoneration of the wrongly accused.

In addition to the location where the sexual assault occurred, the patient (victim) is an important crime scene.  With the advances in DNA evidence collection, the patient may in fact be the most important crime scene in a sexual assault investigation.  It is thus important that you take every step possible to ensure that the medical evidence is not missed or lost, so that ‘chain of custody’ is kept intact.

Your contribution is a key success factor in ensuring that the forensic evidence is correctly collected that can in turn ultimately lead to the prosecution of the perpetrator or the exoneration of the wrongly accused.

 

Examination Principles And Procedures

It is important to observe the following general principles and procedures throughout the evidence collection process:

• Whether sexual assault actually occurred is a legal matter for a court decision and is NOT A MEDICAL DIAGNOSIS. The outcome of any subsequent trial will pivot on any information and evidence provided by physician and the victim’s testimony. Careful recording of medical and legal information can eliminate the need for physician court appearance.”
• Before starting the evidence collection, take time to explain all the procedures to your patient and why they are necessary.  Give your patient a chance to ask any questions.
• Allow the patient to have a family member or friend present throughout the evidence collection, if she so wishes.
• A chaperone for the patient should always be present, especially if the healthcare practitioner is male.  The primary role of the chaperone, preferably a trained healthcare worker, is to provide comfort and support to the patient.  The chaperone also protects the healthcare practitioner in the event of a patient alleging that the examining healthcare practitioner behaved in an unprofessional manner.
• Throughout the evidence collection process inform the patient what you plan to do next and ask permission.  Always let the patient know when and where touching will occur.  Show and explain instruments and collection materials.
• Patients may refuse all or parts of the evidence collection process and you must respect the patient’s decision.  Allowing the patient a degree of control over the evidence collection process is important to her recovery.
• The evidence collection should be performed in a setting that is light, warm, clean and private.  Ideally, the examination environment should provide both auditory and physical privacy, with separate areas for undressing (e.g. behind a screen or curtain, or another room) and the seating aligned so as to allow the healthcare practitioner to approach from the patient’s side.  A gown should be provided.
• If the clothing removed was that worn during the assault and forensic evidence is to be collected, the patient needs to undress over a white sheet or large piece of light paper.  Try to provide as much privacy as possible while the patient is undressing.  Use a cover gown.  If the patient has consented to the collection of her clothing then each item of clothing must be placed by the examiner’s gloved hand into a separate paper bag.  If clothing is to be held for forensic examination, replacement clothing needs to be provided (if possible).
• Both medical and forensic samples should be collected during the course of the examination.  Providing medical and legal (forensic) services simultaneously, i.e. at the same time, in the same place and by the same person, reduces the number of examinations the patient has to undergo and can ensure the needs of the patient are addressed more comprehensively.
• The following universal precautions should be observed at all times during the examination:
  • wear gloves whenever in contact with blood or other body fluids;
  • change gloves between patients; it may sometimes be necessary to change gloves during the evidence collection in order to prevent contamination;
  • wash hands with soap and water after any exposure to body fluids or blood, between patients, and after removing gloves;
  • wear protective eye-wear, masks or face shields if there is a possibility of splashing blood or body fluids into your eyes, face or mouth.
• The healthcare practitioner should document all findings and activities (J88 & ECF) as the evidence collection proceeds.  The patient can thus expect periods of silence during the course of the evidence collection.  Make sure that the patient understands that she can stop the procedure at any stage if it is uncomfortable for her and give her ample opportunity to stop the evidence collection process, if necessary.
• Always address patient questions and concerns in a non-judgmental, emphatic manner.  Use a calm tone of voice.

 

Instructions To The Patient

Should an individual who has been sexually assaulted phone you, it is important to inform the individual of some basic guidelines.

Send the individual to the nearest police station to report the incident in order for an official case to be opened.  Only then can the collection of physical evidence proceed.  This will ensure that the necessary evidence collection kits are obtained.

It is important to advise the individual NOT to do any of the following:

• Change or wash clothing
• Shower, bathe, douche, or wipe
• Wash hands or clean fingernails
• Eat, drink, or smoke
• Brush teeth or rinse mouth
• Touch or remove anything from the crime scene
• Empty the garbage can or bag
• Flush the toilet
• If possible not to urinate or defecate. If the patient must urinate before a urine sample can be obtained he/she must urinate in a clean jar or in a container with a lid.

Request the individual to bring along a set of replacement clothing, including shoes, if possible.

Note: If the individual has done any of the above, document it, and still proceed with the evidence collection.

 

Obtaining Consent

Obtaining a patient’s written consent prior to conducting a medical examination or administering treatment is standard medical practice.  With the advent of evidence collection requirements and crisis intervention services, sexual assault patients are expected to make a decision about consent to these procedures as well.

Informed consent should be a continuing process that involves more than obtaining a signature on the Collection of Forensic DNA Evidence from a Patient form.  When under stress, many patients may not always understand or remember the reason for, or significance of unfamiliar, embarrassing and sometimes intimidating procedures.  Therefore, all procedures should be explained as thoroughly as possible, so that the patient understands what the attending medical personnel are doing and why.  Particular emphasis should be placed on the matter of the release of information to other parties, including the police.  This User Guide and Collection of Forensic DNA Evidence from a Patient form are designed to accompany this protocol and may be used to explain the evidence collection process to the patient.

When written consent is obtained, it should not be interpreted as a ‘blank check’ for collecting evidence.  If a patient expresses resistance or non co-operation, the healthcare practitioner should immediately discontinue that STEP or part of that STEP of the evidence collection process and consider going back to it at a later time during the examination, should the patient then agree.  In either event, the patient should have the right to decline one or more STEPs or parts of STEPs or to decline to answer any question.  Having a sense of control is an important part of the healing process for these patients, especially at the early stages of examination.

It is important to remember that consent to have a support person present must be given by the patient prior to the introduction of that person.  Also, at any time throughout the evidence collection process, the patient should have the right to refuse further interaction with the designated support person and/or request that the support person leave.

 

What Is DNA?

DNA is the most powerful tool ever discovered to solve and prevent crimes and exonerate the innocent.  It is the fingerprint of the 21st century.  We owe it to the thousands of sexual assault victims in this country whose cases can be solved by correctly collecting DNA samples.

Biological evidence consists of body fluids and tissues.  Biological evidence has particular significance since DNA analysis can be conducted in many instances.  Examples of biological evidence containing DNA include blood, saliva, semen, sloughed skin cells and hair roots.

Why Collect Evidence?

The rational for collecting forensic evidence is to link a suspect to the patient (victim of the crime).

Collect As Much As Possible

You only have this one opportunity. Not all samples may turn out to be the suspected sample, so play safe and sample as much as possible.

Collect As Soon As Possible

Because DNA evidence deteriorates with time, it is important to perform your evidence gathering from your patient as soon as possible.

 

Persistence Of Body Fluids

Body fluids such as blood or semen are likely to remain stuck on the patient’s skin if they become air-dried and are not washed off or absorbed by materials such as clothing or bedding.  Saliva may evaporate but will leave cells from the oral mucosa behind.  The length of time that spermatozoa will last in a patient will depend upon where it is deposited on the body.

Collect forensic evidence as early as possible.

 

Persistence Of Spermatozoa

Normally we work on a cut-off limit of 72 hours for samples collected from the body and months or even years to collect from clothes that were worn during or just after the assault.

While 72 – 96 hours might be used as a general guideline, best practice dictates that every sexual assault must be evaluated on a case by case basis by the evidence collector.

Complete sampling

72 hours – World Health Organisation (2003)

72 hours American/Canadian SANE/SART Protocol (2007)

72 hours – Danish Medico-Legal Procedure (2008)

96 hours – Norwegian recommendations (2007)

240 hours – Swedish National Guidelines (2008)

Oral sample

24 hours – Forensic & Medical Sexual Assault Care, Australia (2008)

48 hours – Faculty of Forensic and Legal Medicine, Britain (2007)

Skin swabs

72 hours (unless washed) – Forensic & Medical Sexual Assault Care, Australia (2008)

Until washed – Faculty of Forensic and Legal Medicine, Britain (2007)

 

DNA Evidence Under Fingernails

Swabbing the underside of the nail is better than nail cuttings which is better than nail scraping.  Collect swabs if there is an allegation of struggling, fighting, scratching and/or hand contact with wet semen.

Persistence of skin cells / DNA under fingernails is up to 24 hours (Forensic Science Services UK) Dependent on length of fingernails, washing etc.

 

Persistence Of Salivary DNA¹

Saliva is a composite fluid comprised of water, electrolytes, a glycoprotein (mucin), enzymes, inorganic components, and buccal epithelial cells.  DNA is not present in the liquid saliva but in the cellular material, such as epithelial cells and glandular cells, that are naturally sloughed from the inner lining of the mouth.  The analysis of salivary DNA on evidential material, such as skin or clothing, can provide important information to the forensic scientist.  Transfer may be attributable to spitting, kissing, licking, biting, and sucking.  Frequently in sexual assault cases, the victim has been bitten and, traditionally, bite mark analysis is the main source of evidence.

Salivary DNA will persist on skin for at least up to 96 hours.  Dried salivary DNA will transfer from skin to material (fabric) in contact with the skin (secondary transfer).

Several techniques have been used in the past to find the best method of recovering saliva from human skin.  Traditional methods involve using a single polyester swab moistened with water to recover saliva.  This was later modified by the use of a wet swab followed by a dry swab known as the double-swab technique.  A recent study compared the single- and double-swab techniques and found no significant difference between the two methods.

1                      The Recovery and Persistence of Salivary DNA on Human Skin, J Forensic Sci, 2010, June Kenna, Maureen Smyth, Louise McKenna, Clare Dockery, and Seµn D. McDermott

 

Semen

Understand the importance of semen evidence

The relevance of semen evidence in cases involving male suspects covers the spectrum, depending upon case facts.

 

Semen is composed of cellular and liquid components known as spermatozoa (sperm) and seminal fluid.

Semen evidence can be useful because it is positive identification that ejaculation occurred, and it can be used to positively identify suspects.  However, it is critical to note that failure to recover semen is not an indication that a sexual assault did not occur.  There are a number of reasons why semen might not be recovered in these cases:  Perpetrators may have used condoms, ejaculated somewhere other than in an orifice or on patients’ clothes or bodies, or not ejaculated at all.  Semen may have been depleted by frequent ejaculation prior to the sample in question.  Chronic alcohol or drug abuse, chemotherapy, cancer, infection (e.g., mumps or tuberculosis), or congenital abnormalities also may suppress semen production.

Other factors may contribute to the absence of detectable amounts of semen evidence.  For example, significant time delays between the assault and collection of evidence may cause loss of semen evidence, semen may be washed away prior to the evidence collection or improperly collected, and an object other than a penis may have been used for penetration.

Taking Of Swabs

In order to collect suitable forensic evidence, the healthcare practitioner must understand the types of evidence that may be present in sexual assault cases.

The purpose of taking swabs is to collect samples of any body fluids that may have been deposited on the outside of the patient’s body which may assist to connect the perpetrator with the alleged assault through DNA analysis of the samples.

The area of the body from which the samples are taken may help to corroborate the patient’s version of the events that are alleged to have occurred.  These areas include the exterior of the vagina (for evidence of saliva) if oral sex was performed; the areas around the areola or breast if they were bitten, licked or sucked by the perpetrator (for evidence of saliva); the face, neck, cheeks or lips of the mouth if they were kissed or licked by the perpetrator (for evidence of saliva); any areas of the body, head or limbs on which the perpetrator may have ejaculated (for evidence of semen); and under the fingernails where the patient may have scratched the perpetrator (for evidence of skin cells and blood).

 

Two Types Of Swabs

Two types of swab are present in this kit.  Those with pointed tips and those with rounded tips.  The pointed tipped swabs are specialised swabs that are being used to collect evidence that is found under the fingernails.  The pointed tip ensures that the nail and nail bed is not injured during evidence collection.  The packaging of the pointed swabs is labeled “pointed swab” to distinguish it from the other swabs.  The round tipped swabs are being used to collect all the other evidence.

Wet or Dry swabbing

If the biological stain is dry the swab must be moistened with 3 – 4 droplets of the supplied sterile water before swabbing commences.  The swab must only be moist and not saturated with water.  The reason for this is that it will lead to the dilution of the collected sample or at the extreme the sample may be washed away.

As you will notice the droplets from the supplied water vials are small to ensure that the swab can controllably moisten.  Certain water vials are producing large water droplets that are saturating the swab.

If the biological stain is still wet the swab must be dry during the swabbing procedure.

One Swab, One Stain

For each individual stain that must be collected you must use a separate swab.  If two individual stains are collected with the same swab it can lead to cross-contamination due to the fact that one stain can be from your patient and the other stain can be from the perpetrator.  This can have a negative effect on the results being obtained after DNA analysis.  The swab must be packaged into an Easi Swab Store™ before the next swab is retrieved for evidence collection purposes.

30 – 50° Angle

Hold the swab at a 30 – 50° angle to the surface being swabbed to ensure that the collected sample is concentrated on the tip of the swab.

Rotate

While swabbing rotate the swab so that the sample is evenly distributed around the tip of the swab.

15 – 30 seconds

Continue swabbing for at least 15 seconds to ensure that as much as possible of the sample is collected.

Press Firmly

Press firmly to collect the sample.  Do not press to hard as this may destroy the structure of the swab head or injury your patient.

Never touch the head of the swab

Under no circumstances touch the head of a swab, even with a gloved finger – it can lead to contamination.  Do not touch the head when the swab is removed from its packaging, during the evidence collection process, or during the packaging process.

 

Evidentiary Value Of Body Fluids on your Patient’s Body

If your patient is injured and she bleeds on herself it will be of no evidentiary value to collect that blood.  If your patient where bitten during the incident and any skin were broken avoid the broken areas and any blood in the vicinity of the bite mark.

You only want to collect the saliva of the perpetrator.

Try to locate semen on your patient’s body if the perpetrator has ejaculated on the outside.  Again be guided by your patient in the location of the semen.  Sometimes it is possible to see semen as a whitish crust on your patient’s body.

Your patient’s history must guide you if it is necessary to swab for saliva.  Saliva is not visible to the eye and the act that occurred must guide you where to swab for the saliva.

Body fluid on body swabs

It is very important to indicate if you expect the collection to be semen, saliva or blood.  Normally it will be easy to identify blood.  For determining if it is semen or saliva you must be guided by the information conveyed to you by your patient.

 

Specific Situation – Bite Mark Evidence

In struggles between perpetrators and victims, there is a tendency for teeth (human dentition) to be used as a weapon of attack or defense.  Sometimes it is the only defensive tactic for a victim to inflict serious injury on the perpetrator.  It is a well known fact, that in sexual attacks including sexual homicide, rape and child sexual abuse, the perpetrators more often than not bite their victims.  This can be viewed as an expression of dominance, rage and animalistic behaviour.

Human bite marks are found when teeth are used as weapons.  They can be used as weapons of anger; weapons of excitement; weapons of control or weapons of destruction.  Bite marks are usually found on the skin of the victim. Females are usually bitten on the breasts and legs during sexual attacks, while men are usually bitten on the arms or shoulders and when in defensive postures bites can be found on the hands and arms.

Analysis of salivary DNA evidence from a bite mark on a body submerged in water.Journal of Forensic Science, 1999 Sep; 44(5): 1069-72, Sweet D, Shutler GG.A female body was recovered after approximately 5.5 hours in a river with slow-moving current.  On the victim’s right breast, a patterned injury was discovered and determined to be from human adult teeth.  Evidence was collected according to established techniques including recovery of saliva from the bite mark area despite the body being found submerged in water.  DNA analysis by PCR using polymorphic STR markers revealed a DNA profile of mixed origin.  In addition to the victim’s DNA profile, a genotype contribution from the perpetrator was identified as a minor component.  The DNA typing results from the bite mark correlated with the DNA typing results obtained from other biological trace evidence identified from the victim’s genital samples.  The bite mark and the DNA evidence were used to screen suspects and played an important role in obtaining resolution of this case.  Consequently, it is advisable that investigators routinely swab for salivary DNA in bite mark cases, even when the amount is thought to be minimal.

 

Bite marks can be found in cases of sexual violence in typical areas of the human body – genitals and breasts –, but also in cases of child abuse and other violent crime, and should not be overlooked as important evidence.  In such cases the number of the bites obtained can be very high.  Saliva, like semen and blood, may demonstrate the DNA profile of the individual from whom it originated.

Bite mark impressions can be compared with the teeth of a suspect and can sometimes become as important for identification purposes as fingerprint evidence.

The collection of saliva and the taking of photographs of the affected area are the minimum procedure, which should be followed in cases where a bite mark is present.

Attending Personnel

The only people who should be present with the adult patient in the examining room are the healthcare practitioner, attending nurse, and with the consent of the patient, a trained support person.  Although every effort should be made to limit the number of people in attendance during the examination, there may be instances when a patient requests the presence of a close friend or family member.  If at all possible, these requests should be honored.  Every person in the room can be considered a witness to the procedure and therefore called to testify in court.

There is no medical or legal reason for a law enforcement representative, male or female, to be present to observe evidence collection procedures to maintain the chain of evidence or custody.  This is the function of the attending medical personnel.  Subjecting sexual assault patients to the observation of law enforcement personnel during this process as well as having a law enforcement representative privy to the private communications between the patient and the examining/support team, is an invasion of the patient’s privacy and is an unnecessary practice.

 

Preserving The Integrity Of Evidence

This is necessary in order to maintain the legally necessary “chain of evidence’; sometimes called ‘chain of custody’, or ‘chain of possession’.

The custody of any evidence collection kit and the samples it contains must be accounted for from the moment of collection until the moment it is introduced in court as evidence.  The chain of custody of evidence is a record of individuals who have had physical possession of the evidence.  Documentation is critical to maintaining the integrity of the chain of custody.  Maintaining the chain of custody is vital for any type of evidence.  Therefore, anyone who handles evidence items should be identified, the date noted, source of the samples collected indicated as well as stating, the name of attending personnel and the patient.  All outside containers should be sealed with an integrity seal.  In addition, if laboratory analysis reveals that DNA evidence was contaminated, it may be necessary to identify persons who have handled that evidence.  An identifiable person must always have the physical custody of a piece of evidence.  In practice, this means that the evidence collector will take charge of a piece of evidence, document its collection, and hand it over to a law enforcement officer or store it in a secure place under lock and key.  These transactions, and every succeeding transaction between the collection of the evidence and its appearance in court, should be completely documented chronologically in order to withstand legal challenges to the authenticity of the evidence.

All these are addressed by this kit and the Collection of Forensic DNA Evidence form.

 

Contamination

Contamination is when DNA evidence gets mixed with DNA from another source.

Prevent contamination

During sample collection, there are steps that must be taken to avoid contamination:

• Disposable Powder-free gloves should be used and changed frequently to avoid cross-contamination of evidence.
• When collecting swabs, the healthcare practitioner should take special care not to contaminate the individual collections with secretions or matter from other nearby structures.  Such contamination may unnecessarily jeopardize the integrity of the evidence and future court proceedings.
• While collecting a sample don’t talk over it. If necessary wear a face mask.
• With this in mind, it is preferable to collect the samples in a low traffic area.
• Do not open the swab packaging until it is time for the collection of the swab.  Opening the package too early introduces additional opportunities for the swab to be contaminated.
• After the swab is collected, place the swab in the Easi Swab Store™ immediately versus placing it on any kind of surface.  The goal is to protect the swab from contaminants.

Photography

Photographic reference pictures can be very powerful and useful at a later stage in the investigation if the patient shows signs or injury of an unusual nature.

Photography is recommended when marks such as bite marks and bruises are found on the body.

It is important that photographs of marks such as bruising and bite marks be taken properly.  An individual, deemed appropriate for the situation and who has sufficient photography skills, should be contacted immediately to take photographs of the bite mark evidence.

To demonstrate the size of the bite mark, a clean Ruler should be placed adjacent to – but not covering – the bite mark.  The bite mark should then be photographed.  In order to show different signs of bite marks and bruising and to prevent the camera’s flash from ‘washing out’ the bruise, it is recommended that at least three photographs be taken of each target area: (1) straight on; (2) at a slight angle; and (3) at an increased angle.  For close-up photographs a macro lens is recommended.

 

Do Not Mix And Match

Each evidence collection kit has a unique set of barcodes and components from different evidence collection kits and must never be mixed and matched.

Please Note:

A small square sticker now shows the kit name and the date of kit manufacture.