The headlines are familiar: Another inmate is freed after being cleared by DNA testing. Ever wonder why so many innocent people were behind bars in the first place?

Experts say it’s often mistaken eyewitness testimony that puts innocent people in prison … and lets the real criminal roam free.

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Experts say the problem is that, unlike in the movies, witnesses who point at a defendant and say “that’s him” are often mistaken.

“Eyewitness testimony is the worst evidence you could possibly have, but at trial it’s the strongest evidence you could possibly present,” says David Odom, who represents a man who spent 15 years behind bars because of mistaken eyewitness testimony. “It’s extremely powerful testimony.”

And it’s a problem that has defense attorneys and prosecutors concerned.

“Everyone in both law enforcement and, of course on the defense side, is becoming much more interested in first of all, how can you avoid using eyewitness testimony in the first place, and secondly, how you can avoid using mistaken identity,” Doyle says.

Procedural Problems

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Complicating police procedures are other effects on memory.

“The passage of time, I think, is one of the most important factors in determining the accuracy of an eyewitness,” says Kathy Pezdek, a psychology professor at the Claremont Graduate School in California, referring to the amount of time that elapses between when the event occurs and when the witness makes an identification.

Other factors include the extreme level of stress in the situation, the presence of a weapon, the length of time that the person sees the perpetrator, whether it was dark out, the way witnesses might talk to one another after the event, possible influence by media reports and the race of the witness and perpetrator. Pezdek says more than a dozen studies have now found that there’s an average of about 15 percent difference between the accuracy rates of identifying people of your own race vs. identifying people of a different race.

But even with all the potential margins for error, eyewitness testimony can still make or break a case. Confidence in the police station can translate on the stand, and a witness who honestly believes he or she has identified the right person and says something like “I know that’s him … I’ll never forget that face” can lead to conviction because juries tend to believe confidence equals accuracy.

“A confident witness — particularly one who’s got details and expresses that detail in a confident manner — can be very persuasive,” says Elizabeth Loftus, a psychology professor at the University of Washington who has spent 20 years studying eyewitness testimony and memory.

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Source:

By Amy Sinatra
ABCNEWS.com