The problem of eyewitness unreliability (and memory unreliability) has been known in academia for years; psychologists have long documented how sincere, honest people make important mistakes when reporting what they saw. But it's only recently that the legal system has recognized - and taken steps to mitigate - the problem of eyewitness misidentification.
Consider a few cases that were started (or fueled) by mistaken eyewitnesses.
• When Elizabeth Smart was abducted from her Salt Lake City home in 2002, Elizabeth's sister, Mary-Katherine, watched the abduction while pretending to be asleep, and told the police that the abductor was "about 30 or 40 years old, wearing light-colored clothes and a golf hat." Actually, Smart's abductor, Brian David Mitchell, was wearing black (not white), was nearly 50 (not 30 or 40), and was not wearing a golf hat.
• In 2009, six-year-old Falcon Heene caused a national outcry when his father said he'd been accidentally launched into the skies over Colorado in a homemade balloon. Police weren't sure what to make of the case, whether it was a hoax or a mistake, but what convinced them to take the case seriously was the eyewitness account of Falcon's brother Brad. According to Sheriff Jim Alderman, "He said he saw his brother climb into that apparatus and he was very adamant, they interviewed him multiple times and that was his consistent story." It turned out to be a hoax; the eyewitness was wrong (or he lied).