Trace evidence

Sometimes, something contaminated with other materials comes to tremendous help in medicolegal and other forensic investigations.

For example, when a weapon is found stained with the blood of the victim of assault, then it becomes very much reasonable to suspect that, that particular weapon might have been used to injure the victim.

Examples: blood, semen, hair, saliva, nail, clothes, dust and dirt, fingerprint, weapons, tools, Photography, tyre marks, etc

 

Blood group system:

1. ABO system 
2. MNSs system
3. Rh system
4. KELL system
5. Lutheran
6. DUFFY system
7. P system

 

Medico-legal importance of blood grouping:

1. Dispute paternity

2. Dispute maternity: When the same child is claimed by two women, or when two children are interchanged either by accident

3. Crime

4. Identification of a person: When an individual has some rare blood group, he can be identified with certainty.

5. Cause of death can be determined e.g., incompatible blood transfusion. Poisons can be detected in the blood.

6. Sex of a person

7. Stains due to Body Fluids:

The blood group agglutinogens can be demonstrated in stains on clothes due to semen, sweat, saliva, nasal secretion, urine or faeces in persons who are "secretors".

 

Examination of blood:

1. Physical examination

• STAINS FOUND AT THE SCENE OF THE CRIME
• PART OF THE BODY FROM WIDCH STAIN IS DERIVED?
• AGE OF BLOOD STAINS:
• SEX AND AGE OF PERSON:
• LIVING OR DEAD BODY
• SOURCE OF BLOOD:

 

2. Chemical examination:

The chemical tests depend on the presence in the bloodstains of an enzyme peroxidase, which in the presence of hydrogen peroxide, oxidizes the active ingredient of the reagent and produces the characteristic colored compound.

- Benzidine test

- Guaiacum test

- Phenolphthalein test

- Luco-malachite green test

 

3. Microscopic examination

Red blood cells are circular, biconcave, non-nucleated discs in all mammals except camels. In camels, they are oval and biconvex but non-nucleated. In birds, fishes, amphibia, and reptiles, they are oval, biconvex, and nucleated. Pus cells, epithelial cells, bacteria, faecal matter, etc., are sometimes found mixed with blood.

 

4. MICRO-CHEMICAL:

Micro-chemical tests are based on the property of the heme (iron) part of hemoglobin to form characteristic colored crystals with certain reagents.

1) Haemin Crystal Test (Teichmann's test)

2) Haemochromogen Crystal Test (Takayama test)

 

4. Spectroscopic examination

The solution of the blood has the property of absorbing some of the rays from the spectrum, producing characteristic dark absorption bands, which vary with the type of the blood pigment present.

 

5. Serological  examination

A) Immunological Methods:

1) Precipitin Test:

2) ANTI-GLOBULIN CONSUMPTION TEST: (Hemagglutination inhibition test):

3. GEL DIFFUSION:

4) PRECIPITATION-ELECTROPHORESIS:

5) LATEX TEST:

 

B) ISOENZYME METHODS

 

 

 

Source of Bloodstain

MENSTRUAL BLOOD is usually found on female garments, diapers, or pieces of cloth. It is dark and fluid, has a disagreeable smell and the reaction is acid. On microscopic examination, it shows endometrial and vaginal epithelial cells and the number of microorganisms consisting of groups of bacilli and cocci. Trichomonas vaginalis or monilia may be present.

If the blood is from the NOSE, mucus and hair from the nose may be found.

VOMITED BLOOD is of chocolate color and acid in the reaction due to the action of gastric juice.

Blood due to HEMOPTYSIS is bright red and frothy, with an alkaline reaction.

In blood due to RAPE, semen and pubic hair may be found.

Bloodstains due to BOILS AND SORES show a smeared appearance without definite drops of blood and may contain pus cells and bacteria.

 

Information from a blood sample:

1. Whether it is blood or not

2. Whether it is human blood or animal blood

3. Whether it is from a living/dead body.

4. Source of blood:

• Arterial/venous
• Victims or accused
• It is from Injury or hemoptysis, hematemesis, Menstrual blood or blood of miscarriage

5. Sex of a person

6. Blood group of a person

7. Blood contains poison or not

8. Time passed after death

9. Time passed after bleeding eg. Time of injury

10. Whether the bleeding was antemortem or postmortem

 

Identification of person from blood

Determination of species

Determination of sex: By sex chromatin In leukocytes & Davidson’s body in neutrophils

Determination of blood groups

By DNA typing of blood

 

Differences between normal blood and menstrual blood

Traits	Normal/fresh blood	Menstrual blood
Clot Formation	Occur	Not occur
Color	Bright red	Dark red
Odor	No	Fishy odor
Viscosity	Less viscose	More viscose
Reaction	Alkaline	Acidic
Unfertilized ovum	Absent	Present
Presence of endometrial & vaginal epithelial cells	Absent	Present
Presence of microorganisms	Absent expect in diseases	Normally Lactobacilli, Trichomonas vaginalis, Candida albicans, etc present

 

Significance of bloodstain in the sallower of 18 years girl:

1. It may be menstrual blood.

2. It may be due to masturbation

3. It may be due to rape

4. It may be due to accident

5. It may be due to after sexual intercourse

 

Information from a piece of bone:

1. Identification of a person

2. Race

3. Sex 

4. Age

  

Artefact/post-mortem artefact

It is any change caused or features introduced in a body after death, that is likely to lead to misinterpretation of medico-legally significant ante-mortem findings.

- In such cases, the responsibility of the Medical Jurist is very great.

 

Types;

A. Artefacts introduced between death and autopsy: 1. Agonal artefacts 2. Resuscitation artefacts 3. Artefacts due to the handling of the body 4. Artefacts related to rigor mortis 5. Artefacts related top post-mortem lividity 6. Artefacts in brain 7. Artefacts in liver 8. Artefacts due to post-mortem haemorrhage 9. Artefacts due to decomposition 10. Artefacts due to burn 11. Artefacts in firearm wounds 12. Artefacts due to animal and insect bites 13. Artefacts related to hair 14. Artefacts due to chemicals 15. Enabling artefacts 16. Interment and exhumation artefacts 17. Toxicological artefacts

B. Artefacts introduced during autopsy: 1. Air in blood vessels 2. Skull fractures 3. Visceral damages 4. Extravasation of blood 5. Fracture of the hyoid bone 6. Injury to blood vessels 7. Toxicological artefacts

 

Locard’s Principle of Exchange

It states that, when two objects come in contact, there is always transference of material from each other.

Examples: in case of bestiality, presence of animal hair in the genitals of the accused and presence of human semen in the vagina or anal canal of the animal.