The complete test results show this correlation on 16 markers between the child and the tested man to enable a conclusion to be drawn as to whether or not the man is the biological father. Each marker is assigned with a Paternity Index PIwhich is a statistical measure of how powerfully a match at a particular marker indicates paternity.
However, it is important for defense attorneys to know, and to inform the jury, that the techniques used to locate and identify fingerprints are far from a perfect science.
An understanding of how fingerprints are located and lifted can help attorneys recognize if a flawed analysis was performed by investigators or lab technicians. Further, knowledge of the various fingerprint collection techniques is essential to successful cross-examination of crime scene technicians and fingerprint examiners.
This post attempts to provide an overview of the techniques used to locate, lift, and identify a fingerprint.
Locating the fingerprint Locating a fingerprint often requires a vigilant and calculated search. However, in circumstances where the print is visible to the naked eye, finding a fingerprint is relatively easy.
The more intricate searches take place when the print is present on a surface but not visible. The type of fingerprint left behind usually determines the amount of time and effort investigators must put into locating the print.
According to Forensic Science, there are three types of fingerprints. Patent prints are easy to locate since they are visible to the naked eye.
Patent prints occur when someone has a substance on their fingers such as grease, paint, blood, or ink that leaves a visible print on a surface. Plastic prints are also easy to locate but are less common than patent prints since Forensic fingerprinting occur when someone touches an object such as wax, butter, or soap and leaves a three-dimensional impression of the finger on the object.
Latent prints are the most common type of print and take the most effort to locate since they are invisible. Latent prints occur when someone touches any porous or nonporous surface. Investigators often follow a two-phase process when searching for fingerprints.
The first phase involves looking for patent and plastic prints since they are visible. Often times, a flashlight is used during this phase. The second phase involves a blind search for latent prints, according to Scientific Evidence.
To narrow the search, investigators usually focus on the entry and exits points that the suspect used and any items that appear to have been disturbed, such as overturned lamps or possible weapons.
The type of surface being searched for fingerprints often determines the technique employed by investigators. A powder technique is usually used to identify latent prints on nonporous surfaces such as glass, marble, metal, plastic, and finished wood.
Often times, to avoid smudging the print, a magnetic powder technique is used in which the powder is poured on the surface and then spread evenly over the surface using a magnetic force instead of spreading the powder with a brush.
See Forensic Science by D. The color of the powder should contrast with the surface that is being searched to allow better visibility. For example, the investigator should use a white or grey powder if searching a black marble countertop for prints.
See Scientific Evidence by Paul C. Attorneys should find out whether the crime scene technician who collected prints using fingerprint powder used a disposable brush. If a brush is reused in different locations at a crime scene or reused at another crime scene, the brush can transfer trace amounts of DNA evidence.
Another popular technique for fingerprint location and identification used by both lab technicians and investigators at the crime scene is superglue fuming. Superglue fuming is a chemical process that exposes and fixes fingerprints on a nonporous surface.
In the lab, the process works by using an airtight tank, known as a fuming chamber, to heat up superglue liquid cyanoacrylate which releases gases that adhere to the oily residue of print, thereby creating an image of the fingerprint, according to this article.
Superglue fuming can also be performed at the crime scene. Rather than using a fuming chamber, crime scene investigators may use a handheld wand that heats up superglue and a florescent dye, according to Forensic Science by D.
Superglue fuming performed at the crime scene can be vital to preserve prints on items that are being sent to the lab via mail.
One of the drawbacks is that if the evidence is fumed too long, it can distort the print, rendering it useless, according to this article. To read the procedure used by North Carolina State Crime Lab to conduct superglue fuming in a fuming chamber, click here.
To read the procedure used by the North Carolina State Crime Lab to conduct superglue fuming using a portable wand, click here. The powder technique is not as effective on porous surfaces such as fabric, unfinished wood, and paper. Instead, investigators often use chemical methods to locate the print such as iodine fuming, silver nitrate, or ninhydrin.
When one of these chemicals comes into contact with the chemicals present in the fingerprint residue natural oils, fatsthe print become visual. Iodine fuming takes place in a fuming chamber. The process works by heating up solid crystal iodine which creates vapors that adhere to the oily residue of print, producing a brown colored print, according to Forensic Science by D.
One of the drawbacks of using iodine fuming is that the print fades quickly after the fuming takes place and therefore must be photographed quickly. Alternatively, if the print is sprayed with a starch and water solution, it can be preserved for several weeks.CSI Africa promotes honesty and increased efficiency in the workplace.
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For well over a century, fingerprinting has been the accepted verifiable method of personal identification. Early giants in the field like Francis Galton and Sir Edward Richard Henry devised manual classification of fingerprinting groups so that a match could be produced in a timely manner.
The history of Forensic Ballistics or Ballistic Fingerprinting is a rich portrayal of how elementary techniques used by forensic investigators to evaluate crimes involving the use of guns and other firearms evolved over time to encompass more sophisticated methods . The purpose was was to " to frighten [him] out of all thought of repudiating his signature." The native was suitably impressed, and Herschel made a habit of requiring palm prints--and later, simply the prints of the right Index and Middle fingers--on every contract made with the locals.
How does forensic identification work? Any type of organism can be identified by examination of DNA sequences unique to that species.