What do investigators use to find fingerprints
The analyst then relies on his or her experience to make an evaluation of the prints, either to identify a match or exclusion. This assertion, however, is not based on any studies, research, or analysis. In other words, there is no scientific basis for the belief that fingerprints are unique to each person. In fact, a high profile innocence case shows how wrong this assertion is.
In , Brandon Mayfield, an attorney from Oregon, was arrested as a material witness by the FBI because his fingerprint matched a latent found at the scene of the Madrid train bombings. The bombings killed people and injured hundreds more. Therefore, any nondestructive investigations are performed before the evidence is treated with chemicals. For example, a ransom or hold-up note will be examined by a questioned documents expert before being treated with ninhydrin, since some formulations of ninhydrin will cause certain inks to run, thus destroying the writing.
In criminal justice cases, computerized systems are used to search various local, state and national fingerprint databases for potential matches. Many of these systems provide a value indicating how close the match is, based on the algorithm used to perform the search. Fingerprint examiners then review the potential matches and make a final determination. Fingerprint examinations may be conducted by forensic scientists, technicians or police officers; however, the examiner should have the proper training and experience to perform the task.
Currently many agencies require new examiners to have a four-year degree in science biology, chemistry or physics. In addition, agencies may require examiners to become certified by the International Association for Identification IAI. Fingerprint analysis is usually performed by law enforcement agencies or crime laboratories; however, casework may be sent to private companies if there is a need, such as to reduce backlogs, verify results, or handle high-profile cases.
Fingerprint examination involves looking at the quality and quantity of information in order to find agreement or disagreement between the unknown print from the crime scene and known prints on file. To conduct the examination, fingerprint examiners use a small magnifier called a loupe to view minute details minutiae of a print. A pointer called a ridge counter is used to count the friction ridges.
An examiner uses a loupe to view minute details of a fingerprint. Fingerprint examiners use the ACE-V analysis, comparison, evaluation and verification method to reach a determination on each print. Analysis involves assessing a print to determine if it can be used for a comparison. If the print is not suitable for comparison because of inadequate quality or quantity of features, the examination ends and the print is reported as not suitable.
If the print is suitable, the analysis indicates the features to be used in the comparison and their tolerances the amount of variation that will be accepted. The analysis may also uncover physical features such as recurves, deltas, creases and scars that help indicate where to begin the comparison. Comparisons are performed by an analyst who views the known and suspect prints side-by-side. The analyst compares minutiae characteristics and locations to determine if they match.
The distinction between porous and non-porous surfaces is their ability to absorb liquids. Liquids sink in when dropped onto a porous surface, while they sit on top of a non-porous surface. Porous surfaces include paper, cardboard, and untreated wood. Non-porous smooth surfaces include varnished or painted surfaces, plastics, and glass. Non-porous rough surfaces include vinyl, leather, and other textured surfaces. For porous surfaces, scientists sprinkle chemicals such as ninhydrin over the prints and then take photographs of the developing fingerprints.
For non-porous smooth surfaces, experts use powder-and-brush techniques, followed by lifting tape. For rough surfaces, the same powdering process is used, but instead of using regular lifting tape for these prints, scientists use something that will get into the grooves of the surface such as a gel-lifter or Mikrosil a silicone casting material.
Analysis of Collected Prints Once a print is collected, analysis can begin. During analysis, examiners determine whether there is enough information present in the print to be used for identification. This includes determining class and individual characteristics for the unknown print.
Class characteristics are the characteristics that narrow the print down to a group but not an individual. The three fingerprint class types are arches, loops, and whorls. This pattern is characterized by ridges that enter on one side of the print, go up, and exit on the opposite side.
This pattern is characterized by ridges that enter on one side of the print, loop around, and then exit on the same side. Individual characteristics are those characteristics that are unique to an individual. Comparison of Prints After analysis, unknown prints are compared alongside the known prints. The unknown print is the print found at the crime scene, and the known print is the print of a possible suspect.