Used Of Technology In Determining Stains Evidence
What Are Stains?
Stains are usually formed in a particular pattern from any forms of liquid and more specifically the fluid either diluted or saturated, either sticky or non-sticky, either high or low viscosity to certain surfaces or any other materials. Behaviour of the liquid which flows downhill following the effect of gravity causing them to be split into droplets in any directions. It can be a pool, smear, spot or splash. Pool is formed from the liquid or fluid poured through and accumulated. Smears are usually formed by contact of stained object or unstained object and it tends to be superficial with very uneven intensity whilst spots or splashes formed by drops of fluid being hit at surface either perpendicularly or obliquely. The shape and appearance of stains and smears can give useful information about various factors connected with crime e.g. able to indicate the direction in which fluid comes from depending on the angle of impact, velocity, surface texture and drop size of fluid (Pua 2009).
Picture 2 : Examples of Stains
Type Of Stains
Dried Vs Wet
Wet stains could be easily lifted from the surface using dry and sterile swab and every single swabs are closed in a separate tube with proper label whilst dried stains must be treated with care using fairly wet and sterile swab in the same way. There is some different terminology for dried and wet stains e.g. semen is a type of wet stain whilst seminal stain is the respective dried stain (Pua 2009).
Biology Vs Non- Biology
Another type of classification is biological and non-biological stains.
Whilst non-biological stain refers to those chemical compounds like ink, drug, gunshot residues and food stain such as tomato sauce etc. that are not really have identification value but could refine the search of evidences with forensic importance and narrow down the possibility of the intention of crime or cause of death during the investigation. Distinguishing biological and non-biological stains for example blood versus tomato sauce or ink is important and can be done using one of the following blood presumptive tests that either causing color changes such as Kastle-Meyer (KM), TetraMethylBenzidine (TMB), Leucomalachite Green (LMG) or causing fluorescent reaction such as Luminol and Flurescein tests. Nevertheless, there have some elements of interference for each of them (Lyle 2004). To eliminate the interference, another test has to be done at the forensic lab for confirmation such as Teichmann test, Takayama test or spectrophotometric method in which particularly used for blood confirmation.
Human Vs Non – Human
Human and non-human stains can be further determined after confirmation of biological stains, for instance, human blood is comparable to other animal blood. In this case, Precipitin test is used to ascertain that blood is of human origin based on the antigen-antibody complex formation which produces a clearly visible cloudy precipitate. It involves use of human antiserum (serum containing antibodies specific for human antigens) to detect presence of human antigens in 2 ways i.e. either conducted in capillary tube or by cross-over electrophoresis. If result is negative, test can be repeated using antiserum prepared for other animals as antiserum is commercially available for a number of animals such as dog, cat, deer, cow, and sheep.
Type Of Test Available
To determine whether a retrieved sample actually is blood or some other substance, the serologist conducts tests of two basic types including presumptive or screening and confirmatory. Presumptive tests typically are cheaper and faster. When they are positive, presumptive tests indicate likelihood that blood or other fluid is present but don’t establish that as fact. That’s why confirmatory testing then is needed and to be certain. When presumptive tests are negative, blood or other fluid not present, and the more expensive and time-consuming confirmatory tests can be avoided (Lyle 2004).
Blood isn’t the only bodily fluid that can lead investigators to a criminal. Semen, saliva and, in rare cases, vaginal fluid may hold the key to unlocking a crime. During sexual assaults, semen and saliva commonly are transferred to the victim, the victim’s clothing, or nearby surfaces. The first step in locating these bodily fluids is an examination of crime scene with either an ultraviolet or laser light source which causes these fluids to fluoresce or glow as well. These materials must be carefully collected and preserved, because as moist, biological materials, they are susceptible to putrefaction from bacterial growth.
Other presumptive tests search for the presence of two other components of semen viz. spermine and choline. Each of these tests is positive whenever crystals form after the sample is exposed to certain chemicals. Confirmatory testing relies on the presence of spermatozoa using microscopic examination or presence of prostate-specific antigen (PSA) which unaffected by vasectomy (Lyle 2004).
On the other hand, saliva is an important bodily fluid to the forensic pathologist and it can be recovered from bite marks etc. and reveal ABO antigens, blood type and sometimes yield enough DNA source for profiling analysis. Saliva begins the digestive breakdown of starch into its simple sugars viz. maltose and dextrins in the presence of its primary alpha-amylase. Screening tests such as Phadebas Forensic Press test and Pink paper test can be applied, but unfortunately there is no confirmatory test exists for saliva (Lyle 2004).
Detecting vaginal fluid is difficult, but it may be important in non-ejaculatory rapes and penetrations with foreign objects. Swabs may be taken from a suspect’s penis or from any suspected foreign object. Testing depends upon the finding of glycogen-containing epithelial cells.
Periodic Acid-Sciff (PAS) is a reagent that stains glycogen a bright magenta color in the cytoplasm of epithelial cells that line the vagina. However, young girl and postmenopausal women rarely contain glycogen-rich vaginal epithelial cells (Lyle 2004).
As discussed earlier, screening tests such as Luminol and Fluorescein causing blood to fluoresce or glow in the dark under ultraviolet light, revealing blood that can’t be seen with naked eye. Perpetrators often attempt to scrub walls and floors clean, erroneously assuming that if blood can’t be seen, it can’t be found. Fortunately, that isn’t true. The area of distribution is also clearly defined. Spurts, spatters, drag marks, foot and hand prints jump into view for further projection analysis and crime scene reconstruction. Fluorescein better suited for exposing bloodstains because it doesn’t react with household bleach and is thicker fluid that sticks better to vertical surfaces compared to Luminol (Pua 2009).
After all, the main objective of stain evidence is to narrowing down the focus to find whose stain is it belongs to e.g. by determining its ABO blood type using absorption-elution method to draw out the remaining antigens in the dried stains. By simply typing the blood at crime scene or body, investigators narrow their suspect list and completely exonerate some suspects by using population distribution information for the four ABO blood types. It can be further individualized the sample as red blood cells contain more proteins, enzymes and antigens with such catchy names as Duffy, Kell and Kidd and intracellular enzymes such as adenylate kinase, erythrocyte acid phosphatase, and the very useful phosphoglucomutase isoenzymes (PGM). The more factors inherited independently, the more powerful the identification of the sample is.
Approximately 80% – 85% of population is secretors, meaning they emit proteins of their ABO blood type in all bodily fluids including seminal fluid, saliva and tears. ABO types found can be used to eliminate a suspect in a rape, but they can’t accurately identify the individual who secreted them. Hence, DNA testing at 16 loci must be employed to make a conclusive match (Lyle 2004).
- Evidence Act 1950. Law of Malaysia: Incorporating all amendments up to 1 January 2006.
- Lyle, D.P. 2004. Working with Blood and Other Bodily Fluids: Serology. 1st Ed. Forensic for Dummies pg. 213 – 225. Indiana: Wiley Publishing Inc.
- PDRM Forensic Laboratory. 2009. Use of Polylight and Crime-Lite during investigation. National University of Malaysia NX 3033 Physicochemical Evidences.
- Pua Hiang. 2009. Presumptive Tests and Identification of Stains. National University of Malaysia NX 3062 Body Fluid Investigation.
- Pua Hiang. 2009. Receiving, Recording & Examination of Exhibits. National University of Malaysia NX 3062 Body Fluid Investigation.
|Last Reviewed||:||8 September 2015|
|Writer||:||Lai Poh Soon|
|Accreditor||:||Dr. Siew Shueue Feng|