Examination of Faecal Matter As A Forensic Evidence

Faecal matter (or faeces) are the solid or semisolid remains of food that could not be digested in the small intestine. Bacteria in the large intestine further break down the material.Feces contain a relatively small amount of metabolic waste products such an alter form of bilirubin by bacteria, and the dead epithelial cells from the lining of the gut.

Feces are discharged through the anus or cloaca during defecation. About 100 to 250 grams of feces are excreted by a human adult daily.

1. Odour : The distinctive odor of feces is due to sketole, and thiols. These compounds contains sulfur, amines and carboxylic acids. Sketole is produced from tryptophan.
2. Colour : The brown colour of feces is due to the action of bacteria on bilirubin, which is the end product of the breakdown of hemoglobin (red blood cells).

COMPOSITION OF FAECAL MATTER

•  75 % water
• 25 % solid matter
• About 30 % of the solid matter is of dead bacteria
• About 30 % consists of indigestible food matter such as cellulose
• 10 to 20 % is cholesterol and other fats
• 10 to 20 % is inorganic substances such as calcium phosphate and iron phosphate
• 2 to 3 % is protein.
• Cell debris shed from the mucous membrane of the intestinal tract also passes in the waste material, so as bile pigments (bilirubin) and also dead leukocytes (white blood cells).

EXAMINATION OF FAECAL MATTER

A. Physical Appearance

• Colour : Faecal Matter is generally brown in colour due to urobilinogen, in infants it is yellow due to unchanged bilirubin and milk diet.
  Abnormal Color – Yellow, green, blood streak, bright red, black
• Odour: Aromatic due to indole and sketole.
  Increased odour – Excessive Protein Ingestion.
  Rancid – Milk indigestion commonly seen in infants and adults, normal in infants
  Putrid – Severe diarrhea

B.Microscopic Examination

Suspected stains are softened with distilled water, for about half an hour. A small amount of scraping from the stain is transferred on to a microscopic glass slide and a drop of Lugol’s iodine is added to it. The material is then covered with a cover slip and examined under microscope for the detection of undigested food particles, vegetable residues and muscle fibres.

C. Urobilinogen Test

Urobilinogen is formed in the intestine by reduction of bilirubin. Urobilinogen is oxidized to Urobilin, which is soluble in alcohol. This test relies on the formation of a green fluorescent zinc-urobilin complex formed in the presence of neutral alcohol zinc salt.

Reagent preparation:

Procedure

• A portion of the suspected stains is extracted with a little amount of distilled water.
• Add  2-3 drops of solution 1.
• Now add 2-3 drops of solution 3 and shake it thoroughly.
• The supernatant alcohol layer is pipette off in another tube and in then 2-3 drops of solution 2  is added to it.
• Under UV light rose pink colouration with beautiful green fluorescence is observed, that indicates the presence of bilirubin.

Standards and controls

A known fecal stain stained and unstained control should be tested each time the testing is performed. Use distilled water as a negative control.

Note:

This test is considered to be one of the very sensitive and reliable Test for the confirmation of bilirubin. The species of origin of fecal matter however is not detected normally, unless it is contaminated with blood or mucus.

D. Identification of feces by detection of Bacteroides genes

Detection of Bacteroides uniformis, B. vulgatus and B. thetaiotaomicron is aimed by real-time PCR using a gene sequence specific to these bacteria as it is present in abundant quantity in faeces. (Reference paper)

E. DNA Typing

DNA amplification and direct sequencing of a polymorphic segment of mitochondrial DNA is done. Starting from as little as 10 mg wet weight of faeces, DNA is extracted by a variety of protocols and amplified using primers specific to hypervariable region 1 of the mitochondrial control region. The resulting amplification products are sequenced in solid phase using an automated DNA sequencer.

mtDNA sequences generated from the faeces are compared with sequences generated from their respective blood samples. Sequences of faeces and blood samples from the same individual are found to be identical and thus association of the sample can be done. (Reference paper)

FORENSIC SIGNIFICANCE OF FAECAL MATTER

The identification of feces is important evidence in particular crimes, including illegal fly tipping, harassment and sexual assault (particularly in cases of anal sexual assault); a trace of feces derived from the victim on the surface of a condom left at the crime scene can be crucial evidence.

The identification of faecal deposits on clothing occurs frequently in cases involving homosexuality or homosexual assaults. It may also be present at the crime scene because abnormal mental abberration of the perpetrator or simply because of nervousness or natural desire.

If the fecal matter is already present in the crime scene then there is a possibility of transfer of fecal matter through the footwear or even on the garments of the suspect.

In sodomy and bestiality fecal matter as evidence may be found on penile swab as well as in the garments.

Fecal matter also plays a vital role in examination of the drug dependency nature of the suspect. It has also been observed that the color of fecal matter becomes green, black and red due to consumption of various drugs. It can also be used for the purpose of grouping of blood and hence it can help in person’s individualization as well.