Forensics go back a long way in the US. In the 19th century, forensic medicine was a recognized branch of medicine. By 1910, a French criminologist, formulated the basic forensic principle, "Every contact leaves a trace," and established the world's first crime laboratory.
IP reveals that hair has become one of the most common types of trace evidence. It says hair can help rule out certain populations or help identify an unknown victim. The transfer of hair from a victim to a suspect can raise the probability that the victim and perpetrator came in contact.
But IP points out that hair is never used as definitive proof to indicate guilt because visual comparison is subjective. But when hair is used with DNA, it adds, it becomes a powerful tool for an investigator. Today, hair analysis is only done when DNA tests can also be done.
Still, IP cautions that results from hair analysis can be controversial. The factors that affect these results include where on the body the hair was removed, the person's age and race, and even the color. Because standards vary, a single lab can report different results from the same hair sample and false-positives for illegal drugs are not uncommon.
Similar ambiguities regularly occur in the analysis of other crime-scene materials, including fingerprints and teeth.
Experts in fingerprint analysis will tell you no two fingerprints have ever been found identical in many billions of human and automated computer comparisons. Yet there have been errors. This is an oft-repeated art of thje forensics mythology.
- Brandon Mayfield. Brandon Mayfield is an Oregon lawyer who was identified as a participant in the 2004 Madrid train bombings based on a fingerprint match by the FBI. The FBI Latent Print Unit processed a fingerprint collected in Madrid and reported a "100 percent positive" match against one of the 20 fingerprint candidates returned in a search response from their IAFIS -- Integrated Automated Fingerprint Identification System. The FBI initially called it an "absolutely incontrovertible match". Subsequently, however, Spanish National Police examiners suggested that the print did not match Mayfield and after two weeks, identified another man whom they claimed the fingerprint did belong to.
- RamÃ³n SÃ¡nchez , a legal Dominican Republic immigrant to the US, was arrested on July 15, 1995, on a charge of driving while intoxicated. His fingerprints, however, were placed on a card containing the name, Social Security number and other data for one Leo Rosario, who was being processed at the same time. Leo Rosario had been arrested for selling cocaine to an undercover police officer. On October 11, 2000, while returning from a visit to relatives in the Dominican Republic, Rene was mis-identified as Leo Rosario at John F. Kennedy International Airport in New York and arrested. Even though he did not match the physical description of Rosario, the erroneously-cataloged fingerprints were considered to be more reliable.
- Shirley McKie was a police detective in 1997 when she was accused of leaving her thumb print inside a house in Kilmarnock, Scotland where Marion Ross had been murdered. Although McKie denied having been inside the house, she was arrested in a dawn raid the following year and charged with perjury. The only evidence the prosecution had was this 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) would not admit any error, although Scottish first minister Jack McConnell later said it had been an "honest mistake".
- Stephan Cowans was convicted of attempted murder in 1997 after he was accused of shooting a police officer while fleeing a robbery in Roxbury, Massachusetts. He was implicated in the crime by the testimony of two witnesses, one of whom was the victim. There was also a fingerprint on a glass mug from which the assailant had drunk some water and experts testified that the fingerprint belonged to Cowans. He was found guilty and sent to prison for 35 years. Whilst in prison, Cowans earned money cleaning up biohazards until he could afford to have the evidence against him tested for DNA. The DNA did not match his and he was released. He had already served six years in prison when he was released on January 23, 2004.
- Craig D. Harvey . In April 1993, in the New York State Police Troop C scandal, Craig D. Harvey, a New York State Police trooper, was charged with fabricating evidence. Harvey admitted he and another trooper lifted fingerprints from items the suspect, John Spencer, touched while in Troop C headquarters during booking. He attached the fingerprints to evidence cards and later claimed that he had pulled the fingerprints from the scene of the murder. The forged evidence was presented during John Spencer's trial and his subsequent conviction resulted in a term of 50 years to life in prison at his sentencing. Three state troopers were found guilty of fabricating fingerprint evidence and served prison sentences.
According to Wikipedia, the words "reliability" and "validity" have specific meanings to the scientific community. Reliability means that successive tests bring the same results. Validity means that these results are judged to accurately reflect the external criteria being measured.
Although experts are often more comfortable relying on their instincts, this reliance does not always translate into superior predictive ability. For example, in the popular Analysis, Comparison, Evaluation, and Verification (ACE-V) paradigm for fingerprint identification, the verification stage, in which a second examiner confirms the assessment of the original examiner, may increase the consistency of the assessments. But while the verification stage has implications for the reliability of latent print comparisons, it does not assure their validity.