The public thinks of police lineups as a reliable way to catch criminals. TV shows and movies help give them that impression.
But that impression is just wrong. Mistaken eyewitness identification is the number one cause of wrongful convictions in America.
Many pretrial lineups are structured in a way that may prod the witness to pick the wrong guy. Sometimes police design the lineup in a way that singles out the suspect, or make comments that suggest who the witness should pick.
But even if one could design a perfect lineup, human memory would still be imperfect--and witnesses would still have all sorts of psychological motivations to finger the wrong person.
Flawed police lineups are a big concern in the criminal justice community. The National Academy of Sciences recently issued a massive 140-page report on mistaken eyewitness identifications, and measures that police departments and prosecutors can take to reduce them.