Identification of Blood and Biologicals

Is it Blood?

We will spend a lot of time characterizing the patterns that blood makes as a result of traumatic events, but what if you are not sure it is blood that you are observing?

In this section we will determine how to tell if the stains we find are in fact blood.

Is it human blood?

The precipitin test is the test used to determine if the blood is human.

The same principles that we used when studying blood typing help us determine if blood is human.

When human blood is injected into animals (usually rabbits), antibodies form to fight off the invading human blood.

When blood is subjected to this “human antiserum”, it forms a precipitate at the place where they meet.

Precipitin test

Color Tests

Some tests produce a color change of chemicals if they come in contact with blood due to an oxidation reaction with hemoglobin in blood.

In order for the test to be positive, the color change must be rapid.

We will discuss three of these tests…

Kastle-Meyer Test

Phenolphthalein is an indicator that turns bright pink in a basic solution and remains colorless in an acidic solution.

When it reacts with blood, which is slightly basic, it turns pink.

Other materials, like potatoes and horseradish, can also yield a

pink result, but they are unlikely

to be present at a crime scene.

Adler Test

Also known as the benzidine test, this test has been the most extensively used of any presumptive test for blood.

This reaction is usually carried out in an ethanol and acetic acid solution and results in a blue to dark blue color change.

Leucomalachite Green (LMG)

This reagent was also investigated by Adlers, just as the benzidine test.

This dye turns dark green in the presence of heme, or blood.

This reaction is also usually carried out in acetic acid.

Chemiluminescence

This type of test for the presence of blood is typically done when blood is suspected to be at a particular location, but it has been cleaned up.

Luminol and florescein tests make it possible to detect blood in even the smallest quantities…1 in 10,000,000.

However, though both these tests produce light, they do so by different chemical methods.

Luminol

As with the color tests, luminol is applied with an oxidizer to bloodstains to detect stains that are recent to stains that are years old!

Details and outlines of the stain are illuminated for about 30 seconds before they need to be resprayed.

Sperm

The spermatozoan is what is commonly referred to as the sperm cell. It is a flagellated structure.

The head of the sperm contains the cell nucleus and is packed with DNA.

The confirmatory tests for sperm include a class of enzymes called acid phosphatase. They catalyze the hydrolysis of organic phosphates.

Most popular test for sperm

This reaction also promotes a color change. Brentamine Fast Blue B is the preferred

color developer in this case. This test is sensitive to a sample diluted 500

times. In order to test a sample, a piece of

dampened filter paper is pressed against the stain. When the reagent is added, a dark purple color is noted if semen is present.

Prostate Specific Antigen (PSA)

Another test for semen, especially useful when no spermatozoa exist.

The p30 protein or prostate specific antigen is found in seminal fluid. When injected into rabbits, antibodies form. The serum can be used to detect seminal stains.

Two tests are used detect semen unequivocally:

PSA electrophoresis or antibody-antigen-antibody complex.

Another detectionmethod

Sometimes an alternative light

source may be used to detect

a variety of biological evidence such as

latent fingerprints, saliva, semen, blood, drugs, etc.

Collecting Rape Evidence

1) All outer garments worn by people involved should be collected in paper bags separately.

2) Victim should be examined by medical personnel immediately.

3) Paper is put over a sheet on the floor, and victim should disrobe to collect any trace evidence in the paper.

4) The rape kit requires the following to be collected:

Pubic combings Pubic hair reference samples External genital dry-skin areas Vaginal swabs and smears Cervix swabs Rectal swabs Oral swabs and smears Head hairs Blood sample Fingernail scrapings Urine specimen

Date Rape Drugs

GHB- gamma hydroxybutyrate

Rohypnol “roofies” Both are central

nervous system depressants. Both drugs cause dizziness or drowsiness.

Effects are stronger when drug is combined with alcohol.

Side effects are often memory loss, blackouts and disinhibition.

They are odorless, colorless and tasteless so they are easily slipped into drinks.

Sexual Assault and Rape

44% of victims of sexual assault are under the age of 18 80% are under the age of 30 Every 2 minutes, another American is sexually assaulted. There is an average of 237, 868 (age 12 or older) victims of

sexual assault each year. 60% of sexual assaults are not reported to the police 97% of rapists will never spend a day in jail Approximately 2/3 of assaults are committed by someone

known by the victim 38% of rapists are a friend or acquaintance Source: https://www.rainn.org/statistics