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The ‘West Memphis Three’ and combating cognitive biases

The case shows we see what we expect to see. That can mean innocent people go to jail while criminals remain free.

Last week, the “West Memphis Three” were released from prison, having spent half their lives — 18 years — behind bars for crimes they almost certainly didn't commit. So what made prosecutors and investigators sure they had the right guys, and why were those beliefs, once established, so hard to reverse?

So what produces wrongful convictions? At least three of the often-seen causes were present here: dubious forensic science evidence, false confessions and evidence from unreliable jailhouse informants who often have a strong incentive to tell law enforcers what they want to hear.

Cognitive bias helps explain why prosecutors can focus on a suspect (or three) and fail to see the warning signs that they are headed down the wrong path. Cognitive bias is not the same thing as racial bias or personal animus. It's the habit of our brains to let the first fact we encounter guide our evaluation of the second and the third. One false start can lead to a miscarriage of justice more quickly than any of us would like to believe.

In this case, once the cops saw Echols as something of a freak, an odd duck who read about witchcraft, liked Metallica and didn't exactly fit in, the jump from weirdo to likely satanic cult killer was easier than it should have been. Facts that didn't really prove anything were lumped together with suspicions and dubious theories.

We can't eliminate cognitive biases altogether; they're part of how we think. But we can design procedures to reduce their effects on investigators, prosecutors and even jurors. Police departments and prosecutors can and should implement mechanisms explicitly designed to combat it. For example, in every major case, an investigator or prosecutor with no prior involvement could be asked to review the evidence and assess its strengths and weaknesses. Even better would be if this reviewer weren't expected to provide a “neutral” review but instead were assigned the role of devil's advocate, explicitly asked to find the flaws in the prosecutors' theory. In this case, the filmmakers played an equivalent role, but most defendants aren't so lucky.

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