Different Crime Scenarios

As a bloodstain pattern analyst, I would use the ‘fluorescence' and the specific method I would use is the Fluorescein method. The process involves exposing a chemical substance to a short wavelength to produce light if there is a cleaned bloodstain. Fluorescein test is sensitive in detecting enzymes and iron in the red blood cells. If the criminals have cleaned up the bloodstains, the hemassociated molecule will be formed on the substrata (Wonder & Yezzo, 2014). In using this method, Forensic Light Source or Ultra violate Light, Hydrogen and a darkened room are required. Fluorescein method has optical properties which will increase the amount of the signal.

                            

 I would use ‘Rapid immunoassay' in bloodstain identification. This method is highly sensitive where a test strip is used for the reaction of antigens to form a visible reaction. As a trained personnel, I would use this method since it is easily performed and it produces a result in a rapid manner, unlike the DNA quantitation and immunological tests methods. For instance, the DNA quantitation involves the use of DNA sample and human DNA (Wonder & Yezzo, 2014). This method is not effective since the human DNA produces a positive reaction due to DNA fragmentation.  Immunological tests allow the human bloodstain to react with antihuman hemoglobin to produce positive results of the blood stain.  This method is prone to false interpretation and the method may lack biological materials to perform the test.  Hence, immunoassay acts as a detection reagent for detecting blood stains (Wonder & Yezzo, 2014).

 Household chemicals that can react with fluorescence and give false positive include Hydrogen Peroxide, Sodium Hydroxide, and Phthalates. These chemicals react with fluorescein to form a positive reaction which does not prove to be a fluorescein-blood reaction but it is a false positive (Wonder & Yezzo, 2014). The false positive occurs due to inherent fluorescence which comes from Alternate Light Source and this may not help in the identification of bloodstain.

 

Forensic photography provides clear and high-quality images at the crime scene.  Forensic photography is good for legal investigation and visual records and, it gives a clear evidence of the entire investigation. The photographs record the scene, the location and appearance, the condition and dimension of evidence, the witnesses and other relevant things that would help in understanding the scene (Robinson, 2012). Forensic photography provides a complete understanding and an accurate evidence that helps in documenting all reports. Rather than relying on the blood presumptive test alone, scene photography captures every detail.  The presumptive test is important as they provide accurate information about the crime scene which gives the photographer first-hand information.  Photographer gains a complete information and finds the physical evidence to document the first-hand results. The purpose of photographing is to capture the locations and objects and to move beyond the general information to the specific (Robinson, 2012).

 Investigators may come across challenging situations such as being exposed to biohazards-infectious waste such as needles, blades, blood, urine, chemical and physical hazards such as toxic chemicals, contamination of skin, confined space dangers with explosive materials, new dangers due to new technologies, stress due to working long hours and encountering accident victims, among other related challenges (Robinson, 2012). The crime scene technician can address these challenges by learning adequate basic skills based on personal safety and occupational safety to avoid the hazards. Above all, the technicians should wear gloves when collecting evidence and wear protective gear to avoid contact with the harmful chemical substance. Technicians should adhere to safety procedures and provide emergency care to injured people to minimize the contaminating and maximize safety (Robinson, 2012).

 Steps which I would use to photo document the results of presumptive tests include taking photographs in the core areas using close-up perspectives. I would also take numerous photographs in taking footwear impressions, tire impressions, tool marks, and fingerprints. In photo documenting the presumptive results, I would also use a digital camera to produce high-quality pictures (Robinson, 2012).  Another important point is to investigate the evidence collected and the photographing will be based on providing a permanent record and useful information that will assist the detectives and prosecutors. The first step in arriving the scene is to take the photographs as overall views, medium views, and close-up views. I would also take pictures of surrounding areas such as neighboring homes and other objects (Robinson, 2012).

 

The best type of presumptive test is chemiluminescence and fluorescence tests since they are highly sensitive and cost-effective.  It is important to note that the Presumptive Assays requires oxidation-reduction reaction where the reaction changes to lose hydrogen in biochemical reaction and gains oxidants (Stuart, 2014).  The former uses chemical reaction while the former uses light and both are used as detecting methods due to their high sensitivity and selectivity.  It is also important to note that Chemiluminescence has various agents including fluorescein which is used in the biological system. In investigating crimes, both reagents provides a positive reaction when there is a human blood and the methods also detect the locations where there are traces of blood (Stuart, 2014).

 

 

 

                                          

 

 

 

 

Reference

 

Stuart H. James.,  Nordby J. John  &  Suzanne Bell. (2014). Forensic Science: An Introduction to Scientific

and Investigative Techniques, Taylor & Francis

 

Wonder, A. Y., & Yezzo, G. M. (2014). Bloodstain patterns: Identification, interpretation, and application.

Amsterdam : Elsevier,

 

Robinson, E. M. (2012). Introduction to crime scene photography.  Elsevier