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Fingerprint

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This article is about human fingerprints. See also Fingerprint (disambiguation).

A fingerprint is an impression normally made by ink or contaminates transferred from the peaks of friction skin ridges to a relatively smooth surface such as a fingerprint card. These ridges are sometimes known as dermal ridges or dermal papillae. The term fingerprint normally refers to impressions transferred from the pad on the last joint of fingers and thumbs, though fingerprint cards also typically record portions of lower joint areas of the fingers (which are also used to effect identifications). Friction skin ridges are not unique to humans, however, and some species of primate also have friction skin ridges on "fingers" and paws in configurations sometimes similar to human friction ridge skin. Old world monkeys also have friction ridge skin on their tails, possibly associated with use of their tails for gripping during climbing. Friction skin ridges on humans are commonly believed to provide traction for grasping objects. In the over 100 years that fingerprints have been examined and compared, no two areas of friction ridge skin on any two fingers or palms (including between identical twins) have been found to have the same friction ridge characteristics.

The tip of a finger showing the fingerprint.
The same fingerprint as it would be detected on a surface.

Fingerprint Identification

Fingerprint Identification (sometimes referred to as Dactyloscopy) is the process of comparing questioned and known friction skin ridge impressions from fingers, palms, and toes to determine if the impressions are from the same finger (or palm, toe, etc.). The flexibility of friction ridge skin means that no two finger or palm prints are ever exactly alike (never identical in every detail), even two impressions recorded immediately after each other. Fingerprint identification (also referred to individualization) occurs when an expert (or an expert computer system operating under threshold scoring rules) determines that two friction ridge impressions originated from the same finger or palm (or toe, sole) to the exclusion of all others.

Latent Prints

Although the word latent means hidden or invisible, in modern usage for forensic science the term latent prints means any chance or accidental impression left by friction ridge skin on a surface, regardless of whether it is visible or invisible at the time of deposition. Electronic, chemical and physical processing techniques permit visualization of invisible latent print residue whether it is from natural secretions of the eccrine glands present on friction ridge skin (which palmar sweat, but no oils), or whether the impression is in a contaminate such as oil, blood, paint, ink, etc.

Patent Prints

These are prints which are obvious to the human eye and are caused by a transfer of foreign material on the finger, onto a surface. Because they are already visible they need no enhancement, and are photographed instead of being lifted. Where possible, the item containing the print is taken away and looked at by forensic scientists.

Plastic Prints

A plastic print is a print which is defined as a material that can be moulded or modelled. The print is already visible to the human eye, therefore needing no enhancement. Like a latent print, a plastic print is usually photographed as evidence and where possible, the item containing the print is collected. This type of print could also have the ability to be cast.

Classifying fingerprints

There are three basic fingerprint patterns: Arch, Loop and Whorl. There are also more complex classification systems that further break down patterns to plain arches or tented arches. Loops may be radial or ulnar. Whorls also have sub-group classifications including plain whorls, accidental whorls, double loop whorls and central pocket loop whorls.

  • Arch
    Arch
  • Right loop
    Right loop
  • Whorl
    Whorl
  • Tented arch
    Tented arch

Timeline

There is no clear date at which fingerprinting was first used in prehistoric times. However, significant modern dates documenting the use of fingerprints for positive identification are as follows.

Reliability of fingerprinting as an identification method

File:Measuring fingerprints w compass RCMP.jpg
A member of the Royal Canadian Mounted Police demonstrates the location of ridge endings, bifurcations and dots

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Fingerprints collected at a crime scene, or on items of evidence from a crime, can be used in forensic science to identify suspects, victims and other persons who touched a surface. Developed by Jan Evangelista Purkyne in 1823, fingerprint identification emerged as an important system within police agencies in the late 19th century, when it replaced anthropometric measurements as a more reliable method for identifying persons having a prior record, often under an alias name, in a criminal record repository.

The science of fingerprint identification stands out among all other forensic sciences for many reasons, including the following:

  • Has served all governments worldwide during the past 100 years to provide accurate identification of criminals. No two fingerprints have ever been found alike in many billions of human and automated computer comparisons. Fingerprints are the very basis for criminal history foundation at every police agency.
  • Established the first professional certification program for forensic scientists, the IAI's Certified Latent Print Examiner program (in 1977), issuing certification to those meeting stringent criteria and revoking certification for serious errors such as erroneous identifications.
  • Remains the most commonly used forensic evidence worldwide - in most jurisdictions fingerprint examination cases match or outnumber all other forensic examination casework combined.
  • Continues to expand as the premier method for identifying persons, with tens of thousands of persons added to fingerprint repositories daily in America alone - far outdistancing similar databases in growth.
  • Outperforms DNA and all other human identification systems to identify more murderers, rapists and other serious offenders (fingerprints solve ten times more unknown suspect cases than DNA in most jurisdictions).

Although some reporters and exposè authors claim that fingerprints have long enjoyed a mystique of infallibility, the opposite is true. Fingerprint identification was the first forensic discipline (in 1977) to formally institute a professional certification program for individual experts, including a procedure for decertifying those making errors. Other forensic disciplines later followed suit in establishing certification programs whereby certification could be revoked for error.

Fingerprint identification effects far more positive identifications of persons worldwide daily than any other human identification procedure. The American federal government alone effects positive identification of over 70,000 persons most days, including US Visit (Department of Homeland Security) and Federal Bureau of Investigation fingerprint activities. A large percentage of the identifications (approximately 92% of US Visit identifications) are effected in a lights-out (no human involved) computer identification process with 100% accuracy based on only two fingerprints.

As in any field of human endeavor, errors in fingerprint identifications can and do occur. Such errors in fingerprint identification are so rare that when they occur, they normally make headlines worldwide. One of the most famous fingerprint identification mistakes was made by the FBI Laboratory in 2004. Although the FBI Laboratory had previously made about one latent fingerprint identification error each eleven years, the 2004 error was the first instance in the 84 years of the FBI Laboratory's operation when an error was not discovered and corrected before it caused an innocent person to be jailed.

Below are several noteworthy examples of fingerprint errors:

Brandon Mayfield

A case of misidentifying a print: Brandon Mayfield was an Oregon lawyer who was identified as a participant in the Madrid bombing based on a fingerprint match by the FBI. The FBI Latent Print Unit ran the print collected in Madrid and reported a match against one of 20 fingerprint candidates returned in a search response from their Integrated Automated Fingerprint Identification (IAFIS) system. The FBI initially called the match "100 percent positive" and an "absolutely incontrovertible match". The Spanish National Police examiners concluded the prints did not match Mayfield and they eventually identified another man who matched the prints. The FBI later acknowledged they were in error and he was released from custody. In January of 2006, a U. S. Justice Department report was released which faulted the FBI for sloppy work but exonerated them of more serious allegations.

Shirley McKie

A case of misidentifying a print: Shirley McKie was a policewoman in 1997 when she was accused of leaving her thumb print inside a house in Kilmarnock, Scotland where Marion Ross had been murdered. Although PC McKie denied having been inside the house, she was arrested in a dawn raid the following year and charged with perjury. The only evidence was the thumb print allegedly found at the murder scene. Two American experts testified on her behalf at her trial in May 1999 and she was found not guilty. The Scottish Criminal Record Office (SCRO) never admitted a mistake.

On February 7, 2006, McKie was awarded £750,000 in compensation from the Scottish Executive and the SCRO.[1]

Controversy continues to surround the McKie case with calls for the resignations of Scottish ministers and for either a public or a judicial inquiry into the matter.[2]

Stephan Cowans

A case of misidentifying a print: Stephan Cowans was convicted of attempted murder in 1997 after he was accused of the shooting of a police officer while fleeing a robbery in Roxbury, Massachusetts. He was implicated in the crime by the testimony of two witnesses, one of which was the victim. The other evidence was a fingerprint on a coffee cup, and experts testified that the fingerprint belonged to him. He was found guilty and sent to prison with a sentence of 35 years. While in prison he earned money cleaning up biohazards to accrue enough money to have the evidence tested for DNA. The DNA did not match his, he had already served six years in prison before he was released.

William West

A story that some regard as apocryphal circulates about events occurring in the late 19th century when a man was spotted in the incoming prisoner line at the U.S. Penitentiary in Leavenworth, Kansas by a guard who recognized him and thought he was already in the prison population. Upon examination, the incoming prisoner claimed to be named Will West, while the existing prisoner was named William West. According to their Bertillon measurements, they were essentially indistinguishable. Only their fingerprints could readily identify them, and the Bertillon Method was discredited. There is evidence that men named Will and William West were both imprisoned in the Federal Penitentiary in Leavenworth, Kansas, between 1903 and 1909. However, the details of the case are suspicious, especially since they differ between retellings, and the story did not appear in print until 1918. Today, people familiar with the story differ on whether the story was accurate, a test of people (possibly separated twins) who bore a striking resemblance, a test of known twins, or complete fiction.

Footprints

Friction ridge skin present on the soles of the feet and toes (plantar surfaces) is formed with the same uniqueness as ridge detail on fingers and palms (palmar surfaces). When recovered at crime scenes or on items of evidence, sole and toe impressions are used in the same manner as finger and palm prints to effect identifications. Footprint (toe and sole friction ridge skin) evidence has been admitted in US courts since 1934 (People v. Les, 267 Michigan 648, 255 NW 407).

Footprints of infants, along with thumb or index finger prints of mothers, are still commonly recorded in hospitals to assist in verifying the identity of infants. Often, the only identifiable ridge detail in such impressions is from the large toe or adjacent to the large toe, due to the difficulty of recording such fine detail. When legible ridge detail is lacking, DNA is normally effective (except in instances of chimaerism) for indirectly identifying infants by confirming maternity and paternity of an infant's parents.

It is not uncommon for military records of flight personnel to include bare foot inked impressions. Friction ridge skin protected inside flight boots tends to survive the trauma of a plane crash (and accompanying fire) better than fingers. Even though the U.S. Armed Forces DNA Identification Laboratory (AFDIL) stores refrigerated DNA samples from all current active duty and reserve personnel, almost all casualty identifications are effected using fingerprints from military ID card records (live scan fingerprints are recorded at the time such cards are issued). When friction ridge skin is not available from deceased military personnel, DNA and dental records are used to confirm identity.

US Fingerprint Databases

The FBI manages a fingerprint identification system and database called IAFIS, which currently holds the fingerprints and criminal records of over fifty-one million criminal record subjects, and over 1.5 million civil (non-criminal) fingerprint records. US Visit currently holds a repository of over 50 million persons, primarily in the form of two-finger records (by 2008, US Visit is transforming to a system recording FBI-standard tenprint records).

Fingerprint Compression

Most American law enforcement agencies use Wavelet Scalar Quantization (WSQ), a wavelet-based system for efficient storage of compressed fingerprint images at 500 pixels per inch (ppi). WSQ was developed by the FBI, the Los Alamos National Lab, and the National Institute for Standards and Technology (NIST). For fingerprints recorded at 1000 ppi spatial resolution, law enforcement (including the FBI) uses JPEG 2000 instead of WSQ.

Fingerprint locks

In the 2000s, electronic fingerprint readers have been introduced for security applications such as identification of computer users (log-in authentication). However, early devices have been discovered to be vulnerable to quite simple methods of deception, such as fake fingerprints cast in gels. In 2006, fingerprint sensors gained popularity in the notebook PC market. Built-in sensors in ThinkPads, VAIO laptops, and others also double as motion detectors for document scrolling, like the scroll wheel.

See also

News Stories

  • Do fingerprints lie? - The New Yorker
  • New York Times; "Can Prints Lie? Yes, Man Finds To His Dismay. In front of the immigration judge, the tall, muscular man began to weep. No, he had patiently tried to explain, he was not Leo Rosario, a drug dealer and a prime candidate for deportation. He was telling the truth. He was Rene Ramon Sanchez, an auto-body worker and merengue ..."
  • New York Times; July 30, 1993; "Police Investigation Supervisor Admits Faking Fingerprints"

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