Gillebre,
People swear to have witnessed all sorts of crazy stuff in this world. Victims have sworn in courts of law that individual X committed a violent act upon them, only to have it disproved by circumstantial evidence.
You need to do some reading about the reliability of witness testimony. It's about the most unreliable type of evidence there is. Here's one place to start:
http://www.visualexpert.com/Resources/e ... emory.html
Australian eyewitness expert Donald Thomson appeared on a live TV discussion about the unreliability of eyewitness memory. He was later arrested, placed in a lineup and identified by a victim as the man who had raped her. The police charged Thomson although the rape had occurred at the time he was on TV. They dismissed his alibi that he was in plain view of a TV audience and in the company of the other discussants, including an assistant commissioner of police. The policeman taking his statement sneered, "Yes, I suppose you've got Jesus Christ, and the Queen of England, too." Eventually, the investigators discovered that the rapist had attacked the woman as she was watching TV - the very program on which Thompson had appeared. Authorities eventually cleared Thomson. The woman had confused he rapist's face with the face the she had seen on TV. (Baddeley, 2004).
Experiments conclusively demonstrate that eyewitness testimony is highly fallible, particularly when the subject is experiencing some sort of intense emotion.
You'd better hope if you're ever charged with a crime, and an eyewitness is the only evidence against you, that the jury is better informed than you are in regards to just how reliable such testimonies are.
http://writ.news.findlaw.com/dorf/20010516.html The conventional wisdom, particularly among non-lawyers, is that circumstantial evidence is generally less reliable than eyewitness testimony. People sometimes say that a case is "only circumstantial" to mean that the evidence is weak. A strong case, according to this view, includes the testimony of an eyewitness.
In fact, contrary to popular opinion, circumstantial evidence is often extremely reliable. Blood of the victim that makes a DNA match with blood found on the defendant's clothing, credit card records that place the defendant at the scene of the crime, and ballistics analysis that shows a bullet removed from the victim to have been fired from the defendant's gun are all forms of circumstantial evidence. Yet, in the absence of a credible allegation of police tampering, such evidence is usually highly reliable and informative.
At the same time, numerous psychological studies have shown that human beings are not very good at identifying people they saw only once for a relatively short period of time. The studies reveal error rates of as high as fifty percent — a frightening statistic given that many convictions may be based largely or solely on such testimony.
These studies show further that the ability to identify a stranger is diminished by stress (and what crime situation is not intensely stressful?), that cross-racial identifications are especially unreliable, and that contrary to what one might think, those witnesses who claim to be "certain" of their identifications are no better at it than everyone else, just more confident.
http://scienceblogs.com/cortex/2007/05/ ... stimon.php Bad eyewitness identifications contributed to 75 percent of wrongful convictions in cases that were overturned by DNA evidence.
Given these dismal statistics, some states have tried to fix their procedures for eyewitnesses. New Jersey, for example, used to do police lineups the standard way: witnesses identified suspects from an in-person lineup as detectives stood next to them. The police officers would sometimes offer words of encouragement. New Jersey has now done away with the lineup, and instead presents people one after the other. This is supposed to prevent witnesses from making "relative judgments about which individual most looks like the perpetrator."
From the perspective of neuroscience, eyewitness testimony is an extremely unreliable type of evidence. The first reason is that our vision is vulnerable to all sorts of top-down influences, which alter (corrupt, some might say) the actual inputs witnessed by our eye. To paraphrase Paul Simon, "A man sees what he wants to see and disregards the rest." This doesn't mean that our senses aren't rooted in reality, but it does suggest that we shouldn't place too much trust in the details of perception, especially when the event in question happened fast, from a distance, and in bad lighting.
The second reason eyewitness testimony is unreliable has to do with the nature of memory. Neuroscience now knows that every time we remember a memory, that memory is "reconsolidated," slyly remade and reconfigured. The idea of reconsolidation should make us distrustful of our memories. They do not directly represent reality. Instead, they are an imperfect copy of what actually happened, a Xerox of a Xerox of a mimeograph of the original photograph. This directly contradicts an underlying assumption of eyewitness testimony, which assumes that our memories are immutable impressions, locked away in the brain's vast file cabinet. Recalling the memory shouldn't change the original memory.
But it does change the memory. The very act of remembering what you saw changes the neural substrate of the original memory trace. For more on this research, check out the work of Karim Nader.