Polygraph examination is based on the theory that when a person lies he generates stress reflected in the changes of his breathing, heart rate, and perspiration. Physiological reactions in the respiratory, sweat gland, and cardiovascular are recorded during the test. The examination consists of a pre-test interview, an “in test” or the collection of charts, and a post-test where the examiner analyzes the data and gives his opinion.
This investigative tool has eased police work since it can eliminate suspects, determine phony complaints, narrow the focus of investigation, gather more information and evidence, verify truth, detect lies, uncover violent behavior, elicit admission or confession, and protect the innocents from false prosecution.
However, the procedure has some disadvantages that include dependency on the qualification and skills of the examiner, errors do occur when the machine malfunctions, due to insufficient data the examination can be rendered inconclusive, and there are countermeasures to pass the examination through behavioral and chart-recording manipulation. Polygraph examination is not widely accepted because there is no single credible scientific evidence proving its accuracy. Over 250 studies conducted have resulted in mixed findings.
In its 2003 report The Polygraph and Lie Detection, the National Academy of Sciences concluded that overall, the evidence is scanty and scientifically weak…almost a century of research in scientific psychology and physiology provides little basis for the expectation that a polygraph test could have extremely high accuracy. (Moore, Petrie, & Braga, 2003, p. 212). In addition, the Congressional Office of Technology Assessment reported in its 1983 study that no overall measure or single statistic of polygraph validity can be established based on available scientific evidence. (OTA, 1983, ¶8).
Computer Voice Stress Analyzer (CVSA). This computer-based system determines stress in a person’s voice to detect deception. It measures the so called “micro-tremors”, vibrations that accelerates when someone tells a lie. The computer, equipped with special software, assesses the person’s voice and shows any changes in the vibrations. The system can analyze voice patterns that tell the truth with a high peak graph or a jagged plateau showing someone is lying. However, all studies made along the subject revealed no proof confirming the ability of CVSA to identify stress-related changes in the voice.
There has been no independent scientific evidence to indicate that the computer voice analyzer is a valid instrument to detect deception. The only evidence that has been presented and reviewed, to date, consists of testimonials and other anecdotal evidence. (DPOR, 2003, p. 16). Data produced by CVSA are not accurate (only between 37% and 52% according to voice stress research) and have low levels of reliability that may mislead investigators or elicit false confessions. Protecting the Crime Scene.
One of the most important aspects of securing the crime scene is to preserve the scene with minimal contamination and disturbance of physical evidence. (NIJ, 2000, p. 11). After setting up physical barriers that surrounds the area by responding police, investigators can now proceed by examining and documenting the crime scene. The process involves gathering as much information to learn about the crime, trail its source by conducting a “walk-through” of the scene, and collect evidence.
Documenting the crime scene involves videotaping that gives an outlook of what happened, taking photos with still camera for direct comparison situations like comparing fingerprints or shoeprints, and preliminary sketching to measure distances between objects and calculate bullet trajectory angles or reconstruct the crime scene itself. Once the crime scene has been thoroughly documented and evidence recorded, the process of collection begins.
As a general rule, investigators are required always to wear latex gloves, label evidence properly, change gloves and clean tools between items, let wet items like blood or semen dry before packaging, keep evidence in secure location, and package evidence correctly to preserve it for laboratory testing as well as to avoid contamination and cross-contamination. The evidence must be collected in clean, unused, and suitable containers such as packets, envelopes, bags, and plastics. Liquid items can be placed in a leak proof container while evidence from burning debris can be sealed in airtight, clean metal cans.
A chain of custody must be established to trace the chronological history of the evidence. However, the method of collecting varies according to the type of evidence. Before transporting and submitting the evidence to the crime lab or storage facility, each container must be secured. In addition, the container must also have the initials of the person collecting the evidence or entity that has custody of the evidence, date and time of collection, the name of the investigating agency and its case number, the name of the suspect or victim, and description of the evidence.
Latent Fingerprints. A latent print results from the reproduction of friction ridges found on parts of the fingers, hands, and feet. These prints consist of a combination of different chemicals that originate from natural secretions, blood, and contaminants. (Leighton, Schehl, Trozzi, & Wade, 2002, p. 1). The marks are invisible and undergo a series of physical, chemical and electronic procedures designed to uncover the existence of latent impressions. Latent fingerprints can be found in two types of surfaces: non-porous (metal, glass, plastic) and porous (paper, cardboard, wood).
For non-porous, the process involves cyanoacrylate fuming, cyanoacrylate dye, powdering, vacuum metal deposition, fluorescent lighting, and a laser or alternate light source. Processing latent prints in porous surface includes iodine fuming, applying ninhydrin solution, DFO (1, 8-Diazafluoren-9-one), fluorescent lighting, laser or alternate light source like ultraviolet, and physical developer. Once developed, the prints are scanned or photographed where the images are preserved into the computer for enhancement and examination.
The examiner studies the prints using a scientific method called ACE-V (analysis, comparison, evaluation, and verification). He examines fingerprint patterns, the points of identity or the Galton details like ridge endings, dots, and birfurcations (a ridge that divides), and then looks deeper at the ridges to ridge and pore structure, placement and contour. After completing the ACE-V procedure, the result will be entered to the Automated Fingerprint Identification System (AFIS) for a possible match. AFIS is a computer system that searches fingerprint images through a database containing hundreds of thousands of fingerprint cards.
This system is interconnected with other law enforcement agencies throughout the states as well as to The Federal Bureau of Investigation, who has the largest fingerprint database worldwide with over 47 million subjects in its criminal master file. Upon completion of the examination, the examiner will issue a report to the investigator detailing the results. Reference Moore, M. H. , Petrie, C. V. & Braga, A. A. (2003). The Polygraph and Lie Detection. National Research Council.. Committee to Review the Scientific Evidence on the Polygraph. The National Academies Press, Washington, D. C.
ISBN-10: 0309084369 OTA (Office of Technology Assessment). (1983). Scientific Validity of Polygraph Testing: A Research Review and Evaluation. A Technical Memorandum. Washington, D. C. : U. S. Congress. OTA-TM-H-15. Retrieved February 5, 2007, from http://www. fas. org/sgp/othergov/polygraph/ota/conc. html DPOR (Department of Professional and Occupational Regulation). (2003). Study of the Utility and Validity of Voice Stress Analyzers. Board for Professional & Occupational Regulation, Virginia. Retrieved February 5, 2007, from http://www. polygraph. org/images/virginiavoicestressstudy. pdf
NIJ (National Institute of Justice. (2000). Crime Scene Investigation: A Guide for Law Enforcement. Research Report by the Technical Working Group on Crime Scene Investigation. U. S. Department of Justice, Office of Justice Programs. Retrieved February 5, 2007, from http://www. ncjrs. gov/pdffiles1/nij/178280. pdf Leighton, L. D. , Schehl, S. A. , Trozzi, Y. E. & Wade, C. (2002). Processing Guide for Developing Latent Prints. U. S. Department of Justice. Federal Bureau of Investigation, Laboratory Division. Revised edition. Retrieved February 5, 2007, from http://www. fbi. gov/hq/lab/fsc/backissu/jan2001/lpu. pdf