Tuesday, 19 July 2011

C.S.I. Myths and Latent Print Development Techniques: The Reality of Latent Print Recovery

CSI: Crime Scene Investigation first aired on CBS television on Friday, October 6th 2000 (Cohan, 2008) and has been one of the top television shows on the air since then. Currently it is estimated that over 60 million people watch the CSI television show every week (Heinrick, 2006). Since the airing of the first show, America has seen a 250% increase in the amount of programs featuring forensic science as a course of study (Dutelle, 2006). While the show has made “superglue fuming” and “latent prints” household terms, the effect that the show has on the public perception on forensic science can not be ignored.  The show depicts scientific evidence being gathered, processed, and used to solve major crimes. The characters of the show use costly and high techniques to produce compelling evidence connecting a suspect to a specific crime and reconstruct the crime itself all within one hour. The show depicts that forensic evidence is gathered at every crime scene and the evidence, not the actual investigation, solves the criminal case. The show often depicts unrealistic ideas of what surfaces can be printed. 

Latent fingerprints are the most common form of fingerprint evidence and also the one that poses the most problems (Voss-De Haan, 2006). Latent fingerprints consist of a few micrograms of material transferred from the ridge skin to the surface when the fingers touch a surface. This material is a mixture of natural secretions of the body as well as contaminants from the environment (Voss-De Haan, 2006). Most latent prints are made of perspiration, which exudes from the pores of the skin in the ridges of the print (Allen, 2007). Perspiration contains about 98% water, but the mixture of different organic and inorganic compounds vary depending on an individual’s eccrine and apocrine glands (Voss-De Haan, 2006). With this high concentration of water, prints have a tendency to dry out and sometimes disappear completely (Allen, 2007). Life expectancy of a print is unknown on certain surfaces, but the life expancy can be decreased due to real world conditions such as temperature, moisture, and humidity of the surface (Sampson & Sampson, 2005).
Latent fingerprints have three main categories for eight different pattern types. The first category is the arch which comprises of about 5% of all pattern types, this category consists of the plain arch and tented arch pattern type (Coppock, 2001). The loop pattern comprises of about 65% of all pattern types, and this category type consists of the right slope loop and the left slope loop (Coppock, 2001). The third category consists of the whorl, which comprises of about 30% of all pattern types. The whorl category consists of the plain whorl, central pocket loop, double loop, and accidental whorl (Coppock, 2001). The average fingerprint can contain as many as 175 individual ridge characteristics that can distinguish the fingerprint from others (Jones, 2006). However, a print usually found at a crime scene will be a partial print, only representing 20% of a full fingerprint (Jones, 2006).

Prints can be lifted off porous and non-porous surfaces. Porous surfaces would consist of paper, cardboard, and raw wood. The best latent development techniques for porous surfaces are iodine fuming and Ninhydrin techniques (Sirchie, 2002). Iodine fuming works by a mechanism of interaction of physical absorption (Lee & Gaensslen, 2001). When iodine crystals are warmed, they produce a violent iodine vapor that is absorbed by the fingerprint secretion residues. The latent print then takes on an appearance of a yellowish brown color (Lee & Gaensslen, 2001). Ninhydrin, on the other hand is not used in a process of fuming like iodine or Cyanoacrylate (superglue). Ninhydrin is a biological stain that reacts with the amino acid of latent prints. The amino acids form a permanent chemical bond with the Ninhydrin and the latent prints will become visible (Sirchie, 2002). Ninhydrin solutions can be applied by spraying, swabbing, or dipping a surface containing a possible latent print (Lee & Gaensslen, 2001).

Non-porous surfaces include painted wood or metal, glass, plastics, and polished surfaces. The best latent print development techniques for non-porous surfaces are oxide, florescent, magnetic, metallic, or a combination of print powders (Sirchie, 2002). Fingerprint powders rely on the mechanical adherence of powder particles to the moisture and oily components of skin ridge deposits of the latent prints (Lee & Gaensslen, 2001). It should be noted that just because these methods are the reported best technique for recovery of latent prints from porous and non-porous surfaces it does not mean a latent print can be recovered every time, like on CSI.

In a CSI: Crime Scene Investigation episode called “Burked” (Mendelsohn, Zuiker, & Cannon, 2001),  Detective Brass asks a CSI technician, “Can you get a print off those balloons?” The technician replies “I can get a print off of air”. Statements like this one may make viewers believe that fingerprint evidence is always recoverable (VanLaerhoven & Anderson, 2009). Actually, fingerprints may not be available for a number of reasons. Many materials are not conducive to retaining prints and weathering of surfaces may have also removed any prints (VanLaerhoven & Anderson, 2009). Rarely people leave crisp detailed complete latent prints behind that are seen weekly on CSI. It is entirely possible to touch an item and not leave behind a latent print. When most people touch something, they only contact the surface with part of the fingerpad, and often moving their fingers creating a smudged print (VanLaerhoven & Anderson, 2009).  A smudged print can not be used for comparison and hold very little evidentiary value. For example, it is particularly difficult to retrieve a latent print from rough surfaces such as wood, cloth, skin, cardboard, or Styrofoam. Latent prints may also be partial prints, smeared, or on top of each other (Fischer, 2008). Realistically, smooth shinny surfaces are the best sources for clear, complete latent prints suitable for comparison and identification (Fischer, 2008).

In CSI: Crime Scene Investigation episode “Weeping Willows” (Lloyd & Fink, 2005), a CSI technician fumes a .22 pistol and recovers a perfect print off the weapon that leads to a suspect and solves the case. While latent prints can be possibly recovered off a gun barrel, grip, trigger, magazine, or cartridge finding latent prints off firearms are always difficult (Coppock, 2001). The most frequently used method for fuming a firearm is cyanoacrylate fuming. Cyanocrylate fuming reacts with latent print residues to create a visible white plastic-like print appearance (Coppock, 2001). The difficulty with recovering latent prints on firearms occurs for several reasons. On triggers, most surface areas are grooved to ensure a good grip and are small in nature making the recovery of even a partial print difficult. Once a weapon has been fired, the probability of recovering latent prints on working parts of the firearm are low due to the heat expended (Coppock, 2001). Many forensic experts state that the highest success rate for recovering latent prints from a firearm is usually the unfired cartridges from the firearm. The surface area of the unfired cartridge contributes to a higher recovery rate of prints (Coppock, 2001).

In CSI: Crime Scene Investigation “Play with Fire”(Shankar, Lipsitz, & Fink, 2003), CSI Grissom discovers a body in a press box at a high school stadium. He immediately covers the body in a plastic sheet and fumes the deceased and recovers one print that leads to the arrest of the offender. Once again CSI has made a very difficult task appear easy and frequently used. Realistically, human skin is probably one of the most difficult items to process for latent prints. According to an article in the Journal of Forensic Identification, the probability of recovering a latent print of evidentially value off the skin of a deceased individual is approx. 15,000,000 to one (Sampson, 1996). Although the odds are likely that a latent print will not be recovered of human skin, there is an extremely small chance of a latent print recovery. There are over 70 different methods used to process human skin for latent prints, but the most documented successful process has been the use of magnetic powders (Sampson & Sampson, 2005). Cyanoacrylate fuming, iodine fuming, and ninhydrin are a few of the chemicals used for recovery of latent prints off deceased skin. On living skin, the most common techniques for lifting latent prints are magnetic powders, lifting paper, and photography (Morris, 2005). Magnetic powders used in a direct application method have been more successful at the recovery of latent prints, than cyanoacrylate fuming (Sampson & Sampson, 2005). CSI: Crime Scene Investigation demonstrates cyanoacrylate fuming as only way to process prints of a deceased body, when most technicians use magnetic powders. Keys to successful recovery of evidentiary prints are ambient and skin surface temperature, relative humidity, and the scene environment (Sampson & Sampson, 2005). On deceased individuals, once the surface skin temperature gets 89.6 F or higher, the latent residues transform into a liquid state or diffuse, which can wash away prints (Sampson & Sampson, 2005). Obviously, time is an issue in the recovery of latent prints from human skin. Most prints on human skin must be recovered within a few hours of deposit (Morris, 2005). On living human skin, latent prints can be recovered up to 1.5 hours after the prints are placed on the skin. Currently, it is unknown how long a latent print can remain on a deceased body since proper controlling of the body’s environment are critical in the discovery of latent prints (Sampson & Sampson, 2005). A latent print was recovered 5 hours off a deceased individual in a controlled environment in Miami, the longest recorded time to date (Sampson & Sampson, 2005).
CSI: Crime Scene Investigation, although entertaining, is very misleading about the processing and development of latent prints. The show presents improbable forensic latent print recoveries, such as prints from human skin, as a common procedure.  Recent reports indicate that this top-rated show may have a significant impact on the real criminal justice system in the future by creating unrealistic expectations about the field of forensic science and how latent prints can be processed. These unrealistic expectations could impact the way jurors and others view the “how” and “what” of surface areas that might contain latent prints. Unfortunately, these unrealistic expectations can make forensic experts and investigators’ jobs more difficult than it normally is.

Allen, S. (2007, April). Crime Scene Myths. Law & Order, 55(4), 90-94.

Coppock, C. (2001). Contrast: An Investigator’s Basic Reference Guide to Fingerprint Identification Concepts. Springfield, IL: Charles C Thomas.

Cohan, S. (2008). CSI: Crime Scene Investigation. New York: Palgrave Macmillan.

Dutelle, A. (2006, May). The CSI Effect and Your Department. Law & Order, 54(5), 113-114.

Fisher, J. (2008). Fingerprint Identification: Trouble in Paradise. Forensics Under Fire: Are Bad Science and Dueling Experts Corrupting Criminal Justice. New Jersey: Rutgers University Press.

Heinrick, J. (2006). Everyone’s an Expert: The CSI Effect’s Negative Impact on Juries. The Triple Helix. Retrieved October 1, 2009, from www.cspo.org/documents/csieffectheinrick.pdf.

Lee, H. & Gaensslen, R. (2001). Advances in Fingerprint Technology (2nd ed.). Boca Raton: CRC Press.

Lloyd, A. (writer) & Fink, K. (director). (2005). Weeping Willows. In J. Bruckheimer (producer), CSI: Crime Scene Investigation. Los Angeles: CBS Broadcasting Company.

Mendelsohn, C. (writer), Zuiker, A (writer), & Cannon, D. (director). (2001). Burked. In J. Bruckheimer (producer), CSI: Crime Scene Investigation. Los Angeles: CBS Broadcasting Company.

Morris, M. (2005). Casting a Wide Net: Lifting Fingerprints from Difficult Surfaces. Forensic Magazine. Retrieved October 1, 2009, from http://www.forensicmag.com/Article_Print.asp?pid=52.

Sampson, W. (1996). Latent Fingerprint Evidence from Human Skin (Part 1). Journal of Forensic Identification, 46(2), 362-385.

Sampson, W. & Sampson, K. (2005). Recovery of Latent Prints from Human Skin. Journal of Forensic Identification, 55(3), 188-206.

Shankar, N. (writer), Lipsitz, A. (writer), & Fink, K. (director). (2003). Play With Fire. In J. Bruckheimer (producer), CSI: Crime Scene Investigation. Los Angeles: CBS Broadcasting Company.

Sirchie Finger Print Laboratories (2002). Overview of Latent Print Development Techniques. Youngsville, NC: Sirchie.

VanLaerhoven, S. & Anderson, G. (2009). The Science and Careers of CSI. The CSI Effect: Television, Crime, and Governance. New York: Lexington Books.

Voss-De Haan, P. (2006, July-August). Physics and Fingerprints. Contemporary Physics, 47(4), 209-230.

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