Question

Explain why fingerprinting and blood testing are important methods of identification. Articulate the procedure for use of DNA evidence in a criminal investigation.

Answer 1

• Forensic scientists have used fingerprints in criminal investigations as a means of identification for centuries. Fingerprint identification is one of the most important criminal investigation tools due to two features: their persistence and their uniqueness.
• A person’s fingerprints do not change over time. The friction ridges which create fingerprints are formed while inside the womb and grow proportionally as the baby grows. Permanent scarring is the only way a fingerprint can change. In addition, fingerprints are unique to an individual. Even identical twins have different fingerprints.
• The use of blood in forensic analysis is a method for identifying individuals suspected of committing some kinds of crimes.. Paul Uhlenhuth and Karl Landsteiner, two scientists working separately in Germany in the early twentieth century, showed that there are differences in blood between individuals.
• Uhlenhuth developed a technique to identify the existence of antibodies, and Landsteiner and his students showed that humans had distinctly different blood types called A, B, AB, and O. Once doctors differentiated blood into distinct types, they could use that information to safely perform blood transfusions.
• Furthermore, forensic scientists can use that information to exculpate people suspected of some types of crimes, and they can use it to help determine the paternity of children.
• Forensic scientists often use techniques to identify blood types (blood typing) because an individual's blood type isn't affected by disease, drugs, climate, occupation, living conditions, or any other physical circumstances. Additionally, scientists use blood-typing to determine paternity.
• Forensic scientists could definitively compare blood evidence left at a crime scene to the blood of a suspect. Investigators could test whether or not a suspect's blood had the same pattern of clumping reactions as blood left at a crime scene. If not, investigators could exclude a suspect from further investigation.
• As the science behind blood groups became more refined and widespread around the world, the individual states in the US reflected those developments in their laws. They began to pass legislation that allowed courts to order witnesses, in criminal and civil trials, to undergo compulsory blood group testing. Through it continued to be controversial, many forensic scientists used blood group testing until DNA testing, which scientists considered more accurate and reliable, replaced it in the 1980s.
• Sources of DNA Evidence:-The biological material used to determine a DNA profile include blood, semen, saliva, urine, feces, hair, teeth, bone, tissue and cells.
• Samples that May be Used:Investigators collect items that could have been touched or worn by persons involved in a crime. The following items may contain DNA material:Masks,Hats,Gloves,Clothing,Tools,Weapons etc.
• The best evidence occurs when a person’s DNA is found where it is not supposed to be. For example, consider a breaking-and-entering that occurred in a residential area. Near the point of forced entry, a knit cap was found which the homeowners confirm was not theirs. Several head hairs were recovered from the inside, one of which had a root with tissue attached, which made it possible to obtain a DNA profile. The DNA profile was used to identify the perpetrator.
• As technology advances, forensic scientists are able to analyze smaller and smaller biological samples to develop a DNA profile. For example, if a person touched an object or weapon, skin cells may have been left behind.
• This low-level DNA is sometimes referred to as “touch DNA”. It can even be collected from a victim’s skin or bruises where they were handled roughly. Low-level DNA samples may be helpful when examining evidence where it would be difficult to retrieve fingerprints—such as textured surfaces on gun handles or automobile dashboards. However, not all jurisdictions have the capability to process this evidence.
• To compare the victim’s or suspect’s DNA profile to the recovered crime-scene DNA, the laboratory will need to have their known biological samples available for a side-by-side comparison.
• These known samples are called reference samples. In some jurisdictions, a DNA sample is routinely taken from an arrestee during the process of booking and fingerprinting. However, this is an evolving area of law and states vary in their laws governing the collection of DNA from arrestees.
• Sometimes a court order is required to retrieve a reference from a person of interest. Reference samples are always collected from victims unless they choose not to cooperate with the investigation; in that case, a court order might be required.
• Prior to performing DNA analysis at the laboratory, initial testing is often conducted at the crime scene to determine the type of biological material in question. Screening for the presence of biological materials may also be conducted in the laboratory to determine if a specific biological fluid may be present. Most biological screening tests are presumptive in nature and do not specifically identify a bodily fluid.
• To determine who deposited biological material at a crime scene, unknown samples are collected and then compared to known samples taken directly from a suspect or victim.
• Most DNA samples submitted to a laboratory undergo the following process:
• Extraction is the process of releasing the DNA from the cell.
• Quantitation is the process of determining how much DNA you have.
• Amplification is the process of producing multiple copies of the DNA in order to characterize it.
• Separation is the process of separating amplified DNA product to permit subsequent identification.
• Analysis & Interpretation is the process of quantitatively and qualitatively comparing DNA evidence samples to known DNA profiles.
• Quality Assurance is the process of reviewing analyst reports for technical accuracy.