Are witnesses memories of crimes accurate?

This month, the Supreme Court heard its first oral arguments in more than three decades that question the validity of using witness testimony, in a case involving a New Hampshire man convicted of theft, accused by a woman who saw him from a distance in the dead of night.

And in August the New Jersey Supreme Court set new rules to cope with failings in witness accounts, during an appeal by a man picked from a photo lineup, and convicted of manslaughter and weapons possession in a 2003 fatal shooting.

Rather than the centerpiece of prosecution, witness testimony should be viewed more like trace evidence, scientists say, with the same fragility and vulnerability to contamination.

Why is a witness’s account so often unreliable? Partly because the brain does not have a knack for retaining many specifics and is highly susceptible to suggestion. “Memory is weak in eyewitness situations because it’s overloaded,” said Barbara Tversky, a psychology professor at Columbia University’s Teachers College in New York. “An event happens so fast, and when the police question you, you probably weren’t concentrating on the details they’re asking about.”

Even the process of police questioning and prepping for trial can crystallize a person’s own faulty reconstruction. In 2000, Dr. Tversky published a series of experiments conducted at Stanford University in the journal Cognitive Psychology. In one, volunteers read profiles of fictitious roommates with both charming and annoying habits; they were then asked to write either a letter of recommendation or letter making a case for a replacement.

When later asked to repeat the original description, the volunteers’ recollections were skewed by the type of letter they had written. Their minds had shed qualities that didn’t match the first draft of their own recall and had embellished those that did.       
http://www.nytimes.com/2011/11/29/health/the-certainty-of-memory-has-its-day-in-court.html?_r=2&ref=science