''Misidentification is the absolute greatest source of mistaken conviction," said Los Angeles psychologist Robert Shomer, who has testified as a witness identification specialist in more than 400 trials over the past 30 years.
Mistaken witness identifications played a role in the convictions of nearly 80 percent of the 157 people nationwide who have been exonerated by DNA testing, said Jane Fox of the New York-based Innocence Project.
Now, the Virginia State Crime Commission has asked law enforcement agencies to adopt a lineup procedure in which witnesses are shown individual mug shots or suspects one at a time. Advocates of the technique say it can help reduce the tendency to compare and settle.
In 2001, New Jersey became the first state to adopt the technique. The North Carolina Actual Innocence Commission last year began advocating the method. And a handful of jurisdictions, including Boston, Minneapolis, and Santa Clara County, Calif., also have adopted them.
In Virginia, the new guidelines also advocate having the lineup administered by an officer who does not know who the suspect is, to eliminate the possibility that the officer unintentionally influences a witness's choice in a lineup.
''It's almost impossible not to react when a person makes a choice," said eyewitness identification specialist Gary Wells, an Iowa State University psychology professor who helped develop the double-blind sequential method. ''You know your guy is in position three . . . and so if the witness starts showing interest in number two, then your natural reaction is to have a little bit of impatience."
Other cities -- such as New York City, Seattle, and Indianapolis -- have begun using a computer program to present witnesses with photos of suspects, avoiding any possible bias from detectives.
Some prosecutors argue the new methods are unnecessary and can lead to fewer correct identifications.
Robert Horan, the Fairfax County commonwealth's attorney and vice president of the National District Attorneys Association, said the practice of showing groups of photos to a witness is eventually put to the ultimate test: trial.
The witnesses have to testify under oath, Horan said. ''I just don't think people lie about things once they get on the stand," he said.
Marvin Anderson disagreed. Anderson, 41, still remembers the fear he felt when a rape victim in 1982 singled him out of a police lineup as her attacker. The then-19-year-old was convicted largely based on the victim's identification and received a 210-year prison sentence. Paroled in 1997, he became the first Virginian to be cleared of a crime by genetic testing and was officially exonerated in 2001.
''No matter how old I may live to be, those are years that I will never forget," Anderson said of his time behind bars.
The Virginia General Assembly passed two identical bills this year that would require law enforcement agencies to have written policies for conducting lineups.
