Contact Trace evidence may be defined as• Any material which, when left behind at scene or, on the body of victim or assailant or, any other thing that acts as clue and can be presented in the court as an evidence.• THE TRACE EVIDENCE HELPS IDENTIFICATION OBJECTIVELY
• It helps in the recognition of the evidence and its association with a particular:• Person• Thing• Place• and acts as a clue for the identity of that source.
• Trace Evidence is based upon the principal known as, Locard’s Exchange Principal
• Sir Edmond Locard ( 1877 – 1966 )gave two principals, 1. Every contact leaves a trace 2. Exchange of trace is usually a two way process.
• Classical examples of the trace evidence is a cases of: Sexual Assault PHYSICAL ASSAULT
SEXUAL ASSAULT• In which transfer of biological material such as semen, blood, saliva, hair etc. occurs from:• Assailant to Victim• Victim to Assailant• From Assailant & Victim both to the scene of crime• Non Biological Material from the scene of crime to both Assailant and the Victim.
Objectives of Study• 1- Identification of unknown• 2- Confirmation of a previously known identity• An attempt is made to establish similarity or dis-similarity between two or more objects one of which has come from a known source.• Comparing this trace with a control taken from the source from where it is suspected to have come, will confirm the character of a trace and its association is established.
• CLASSIFICATION• Trace evidence may be grouped into:• 1. Biological Evidence• 2. Non-Biological Evidence
Biological Evidence These originates fromhuman, animal or plant sourceand include mainly : 1. Body Fluids 2. Body Tissues 3. Stains
Body fluids• Includes blood, semen, saliva, urine, vomit, cerebro-spinal fluid, etc.• Such fluids may be found in the form of stains at the scene, clothes, and body of victim or assailant.
• Other Biological materials• Human Hair from head and pubes.• Scrapings from the under surface of Nails which contains,• Epithelium of skin of assailant or victim deposited during physical or sexual assault.
Non-Biological Evidence• These comprises of 1. Items of Personal Use 2. Other Materials found in the Environment (Foreign Bodies)
• These Personal Items are Clothes, Spectacles, Purse, Wristwatches, or other things in use.• The Environmental Materials are fibres from carpet, vegetation in the garden, grit particles from the road.• Other Non-Biological materials consists of bottles, tablets, bullets or pellets, weapons of offence or any other thing used in the crime.
Collection, Preservation, & Dispatch of Specimen (Trace Evidence) To Analytical Laboratory
• The scientific study of the specimens pre-requires: 1. Collection of Material from source 2. Its Preservation 3. Despatch to the laboratory
The procedures involved in Medico-Legal cases are different from those involved in the clinical labs and requires special knowledge.• WHY ?• 1. The place of collection / sampling• 2. Interest of parties involved• 3. Safety against tampering• 4. Chain of custody
• The study of trace evidence FOR THE PURPOSE OF UNDERSTANDING is divided into: 1. Pre-Lab work 2. Lab Work
• Pre-Lab Work is further divided into, a) General Instructions, which are applicable to all specimens, and b) Special Instructions, which are specific instructions for each specimens.
1. Consent For Collection• Authority :• Request for collection is made by Police or Magistrate in writing.• Written Consent of the person with signature or thumb impression. If the persons refuses to give consent, then note it down and send the person back to authority.
2. Identification Of Person• Identification is important in both living or dead, which is done by,• a) Subjective• b) Objective• c) Third Party• Two identification marks are noted.
3. Collection of Specimens• The person must have the knowledge as to : a) What is to be collected (source) b) From where to be collected (site) c) How much to be collected (quantity) d) How it is to be collected (procedure)A proper material from a proper site in a proper quantity by a proper method. (proper collection)
4. Collection of SpecimensTo ensure that the collection is proper, it is advised that the process of collection should be divided into various stages and each phase has its own limited goals.These phases areOverview PhaseDetailed discovery Search phaseRecovery PhaseReview Phase
1- Overview PhaseIn this phase the examiner should gothrough the history of the case, studythe documents and visit the scene ofcrime and should have an overallview of the scene of crime, positionof body, location of objects, etc.
2- Detailed discovery Search phase In this phase the examiner should concentrate on the areas of interest and should search for the evidence by walking through the area from end to end twice, move the things, move the body to look underneath body etc.
3- Recovery PhaseSpecimens are collected and each item should be identified, noted for its location and if possible be photographed. 4- Review PhaseIn this phase go through all the above three phases and ensure that nothing is left, because if left then it will be left for ever and you may miss some important evidence.
• The specimen may be present in three forms, .Dry form .Wet Form .Mixed with other Articles.
Dry Form– Scrap the specimen and place in a funnel of glazed paper, or– soak the cotton swab in normal saline and apply it over the dry stain, then dry this swab in air and use this swab as specimen.Wet Form-Dry the specimen and then scrap it or wipe itwith wet cotton swab.Mixed Form-Cut that portion and separate it
PACKING• The Material of the Container should be appropriate, Which means it should be chemically inert, generally a Glass container is recommended. But as glass being fragile, plastic containers with lid are also used.• The Size and Shape of the Container should be appropriate, so that material should be easily placed in it.• A proper container, of proper material and proper size (proper packing)
5. Preservation• The preservation of specimens is done normally by two processes,• Desication or Dehydration• Freezing• A proper preservative, in proper quantity having proper concentration. (proper preservation)
Preservation in Different Situations• In Histo-pathological examinations we need a preservative which should preserve & prevent autolysis and harden the tissues.• For Chemical examinations we only require preservation.• For Serological Examinations we also need anti-coagulative activity.
A GOOD PRESERVATIVE• It should be Cheap• It should be Easily Available• It should be also Chemically Inert• It should be Effective for the purpose• It should not react with the container & specimen
Normally used Preservatives are,• For Chemical Analysis, Super-Saturated Saline is used. It acts by de-hydration ie; extracts water from the tissues & they get preserved.• For Histo-pathological Examinations 10% Formal Saline ( ie; 10% folmalin in saturated saline) or 95% Alcohol is used.• For Serological Examinations anti-coagulants used are, Ca. Oxalate, Heparin, etc;
Type Of Material Size & Lids Pre-Analysis Shape servativeChemical Plastic Large Plastic Saturated mouthed Lids Saline JarsHisto- Glass According Glass Lids 10%pathology to size of Formal organ salineSerology Sterilized Test Tube Glass or Anti- glass test Rubber coagulant tube stopper
6. LabellingEach container should be labelled indicating,• Number of jar, 1, 2, 3, ….. Should be mentioned• Name of specimen, site of collection• Preservative used• PMR / MLC no.• Date & Time• Name of Person• Examination required• Name of Doctor, Signature & Official Seal should be affixed.
7. Sealing of Specimens• All the specimens should be sealed with Sealing wax to avoid tempering and to maintain secret chain of custody• All the containers or jars should be packed in one box, and the box should be labelled indicating,• Address to be sent• Arrow showing Upside• Box should be sealed• Box should accompany a forwarding letter
Information To Be Sent Along• The following information is to be sent in the forwarding letter along-with the Specimens,• a) Copy of MLR / PMR• b) Examination required• c) Request letter containing the bio-data, name of specimen, etc;• d) Copy of FIR• e) Copy of Inquest Report• f) Specimen of the Seal
8. Despatch of The Specimens• Specimens should be collected, preserved, and despatched immediately after autopsy.• The only condition in which the specimens are allowed to be kept is that when the autopsy is conducted at odd hours, when the lab is closed.
9. Safe Storage• The specimens should be kept in lock and key in the freezers.• The specimen should be registered• The seal should be intact, it should be compared with the specimen of the seal provided.
10. Transportation• The specimens should be transported,1.Through Police2.Through Railway Parcel3.Through Postal Parcel4.Through Special Messenger by hand.
CHAIN OF CUSTODY• “ Any and all who handle the specimens at a particular instant should be able to certify the extent of handling i.e.• What was collected• Why it was collected• To whom it was handed over• When it was handed over• For how long it remained in custody
• Chain of custody should be maintained to avoid adulteration and tempering,• Chain of custody should be maintained till the specimens are presented in the court• Handling should be certified i.e. It must be on written receipt• Principals of chain of Custody• Shorter the chain, Better it is By involving less and less persons.• Surer the chain, Better it is.• Every surrender should be on a written receipt.
Examination Of Blood Types of Cases Criminal CasesPhysical Assaults, Sexual Assaults, Poisoning (Homicidal, Suicidal, Accidental) Civil Cases Identity of the person Inheritance Disputed Paternity Disputed Maternity
Source of Blood1.External On clothes On the body At the scene of crime (As stains or clotted blood)2. Internal Peripheral veins Direct from heart at autopsy
Special Instructions for Blood collection1. In cases of dry stains on any hard surface, it is scrapped off with the scalpel and collected on a glazed paper.2. In cases where stain is wet, then it can be collected as, a) Let the stain be dried then scrap it. b) A wet cotton bud in normal saline is rolled on the stain, dry this bud in air and then put it in a clean glass test tube, with the care it should not touch the walls.
3. When the blood is on plaster or wood, then cut that portion of wood and chip off the plaster.4. When the blood is on the soil or ground, then sufficient amount of soil is collected.5. When the stain is on clothes, then they are allowed to dry in air, not in heat or sunlight, then pack them in plastic bags separately.
6. Disputed Paternity or Maternity If the specimen is to be collected for disputed paternity or maternity, then is collected from peripheral vein with syringe. No preservative is added except anti-coagulant e.g.; Ca. Oxalate, Heparin The samples of blood are collected in front of all the constesting parties. The sample of father is signed by mother. The sample of mother is signed by father. The sample of child should by both father and mother
7. Poisoning At autopsy the blood is collected direct from heart or big veins bringing blood to the heart.8. CO Poisoning After collecting blood a layer of liquid paraffin is placed over the blood to avoid evaporation.8. Alcohol Intoxication At the site of collection of blood from peripheral vein, the area should not be cleaned with spirit to avoid contamination.9. Quantity of Blood In living persons 10-15 ml and in case of autopsy 50- 100 ml of blood is collected.
EXAMINATION OF SEMEN• It is the most extensively studied material. Semen coagulates immediately after ejaculation and then liquefy in next 15 minutes.• Both these processes are dependant upon different enzymes in semen.• The medico-legal importance of study of semen is in cases of SEXUAL ASSAULTS
Sources of Collection1. External . On the Body . On the Clothing . At the Scene of Crime2. Internal . Pre-Hymenal areas . Post-Hymenal Areas
Collection• 1. The portion of fabric having the stain is cut, dried in shade to prevent putrifection and preserved.• 2. If pubic hair are matted together, a portion of hair is cut and preserved.• 3. Dried or drying seminal stains on the body like, medial aspects of thighs; are collected on soaked cotton swab in saline and then dried.• 4. Dry stains on smooth surface is scrapped with a blunt scalpel into a glass container.
Swab collectionFrom the Genital Area, total 5 swabs arecollected, a) Pre-Hymenal Area, 3 swabs are taken b) Post-Hymenal Area, 2 swabs are taken
Collection of Swabs• Swabs must be taken before the digital examination and before the urine sample.• Check for the AUTHORITY• Take the CONSENT• UNDRESS the patient• Place the patient in LITHOTOMY position• First take Pre-Hymenal Swabs Which are 3 in number
• One is taken from medial sides of thighs.• Second from the area around vulva.• Third from pre hymenal area in the introitus.
Vaginal Swabs• PRECAUTIONS• If the hymen is intact, do not attempt digital examination,• Do not attempt the use of vaginal speculum,• So if hymen is intact no swabs are taken.
• When the patient in lithotomy position, gently separate labia,• Introduce vaginal speculum,• After that cotton swabs are passed through the opening in the speculum, and collect two swabs from high up.
Preparation of Slide• From one vaginal swab which we have collected, slides are prepared,• Swab is rubbed in the middle 1/3 of the slide,• Two slides are prepared,• Slides are dried in air,• Then they are placed facing each other with placing match sticks in between them, so that they should not rub with each other.
Pipette Specimen• The specimen of semen can also be collected from vagina with the help of pippette,• About 20 ml of normal saline is injected into vagina,• After some time the specimen is collected with the help of special pippette, which have a bulb in between to avoid suction into mouth,• Then this specimen is transferred to test tube, for further processing.
• The medico- legal importance of saliva and its trace is in both, SEXUAL ASSAULTS PHYSICAL ASSAULTS
SECRETORS’ Secretors are those persons who secrete theirblood group substances in their bodysecretions, especially SALIVA SEMEN VAGINAL SECRETIONS and TEARS About 80% people are secretors’, and thosewho does not secrete are called non-secretors’.
Source of Salivary StainsIt may be found, a) On Used Articles • CUP OF TEA • POSTAL ENVELOP, etc; b) On The Eaten Food • HALF EATEN FOOD LEFT • EATEN APPLE c) On The Body of Victim • AT THE AREAS OF BITE
On the body of victim, Bites may be, 1) True bites 2) Love BitesTRUE BITES Bites between the teeth, its impression help in identity of the person.LOVE BITES It’s a pressure suction between tongue and teeth, there appear tiny areas of haemorrhages. They are usually found over neck, breasts, chest wall, medial sides of thighs. Salivary stains here will help in identity.
Collection of stains• Soak the cotton swab in normal saline and role it over the stained area, dry it in air and put in test tube.
Collection of Control• The most important thing is to collect control specimen of saliva from the suspect.
Procedure of Collection Of Control Specimen Of Saliva• First ask the patient to wash the mouth with normal saline, then with plain water,• Now ask the individual to chew some inert material, piece of paraffin, non- sugar coated chewing gum,• Then ask the person to loosen his facial and oral musculature,• Tickle the inner walls of mouth with glass rod,• Tilt the mouth on one side, the saliva will start flowing to the angle of mouth,• Collect it in a glass test tube.
Amount to be Collected 50 – 60 mlPreservation of Saliva a) First place the sample test tube in hot water bath for 10 minutes, The enzymes will be inactivated b) Then Centrifuge the specimen at 1500 rev/min for three minutes, Cell debris will settle down and the supernatant is preserves c) No preservative is added.
• The Medico- legal importance of stomach wash and vomitus & its stains is in cases of poisoning.• The stains of vomiting may be present on the clothes & scene of crime, clothes after drying should be packed & sent to chemical examiner’s lab.• Stomach wash is collected in all cases of poisoning, First washings of the stomach should be preserved.• No preservative is added to it.