The Dark Dangers of Tunnel Vision
Why police and prosecutors suspect the wrong person—and then dig in.
In retrospect, it’s clear that police and prosecutors headed off in the wrong direction and then couldn’t see flaws in the theory they’d chosen, or the clues that led elsewhere. The problem isn’t that they started with Michael Morton. Domestic violence statistics show that women are more likely to be killed by their husbands than by someone they don’t know. The problem, rather, is that they ended with Morton. The same also seems true in the case of Cameron Todd Willingham, who was executed in 2004 for the deaths of his three children, based on the theory that he set the fire that burned down his house and killed them. Read David Grann’s amazing New Yorker exposé about the case, and you come away horrified by the class assumptions and shoddy burn-pattern analysis that prosecutors relied on to convict Willingham. And in his new book A Wilderness of Error, Errol Morris makes a strong case for the wrongful conviction of Jeffrey MacDonald, (yes, the subject of Fatal Vision and The Journalist and the Murderer) who remains in prison for the 1970 murder of his wife and two daughters. Once more, the husband MacDonald was the obvious suspect. And like Morton, he appeared unemotional rather than grief-stricken. Investigators didn’t believe his story about a break-in by a bunch of hippies. Feeding their skepticism was a key piece of initial evidence: A coffee table found in the family’s living room lying on its side, which the investigators said couldn’t have fallen that way given its construction. The table was part of the tableaux of disorder MacDonald claimed he woke up to after he’d lost consciousness when he was wounded; if its toppling over was staged, then that called his entire account into doubt. As Morris tells the story to dramatic effect, a military judge later knocked over the table in a test—and the table fell onto its side, exactly as it had been lying in the crime scene. But for MacDonald, this debunking came too late to halt the snowballing suspicion of him, or to persuade prosecutors to take seriously the confession of a woman who matched the description of one of the intruders MacDonald said he saw.
More common ground that Morton and MacDonald share: Their wives were murdered in placid middle-class neighborhoods, in which fears of a dangerous assailant on the loose was only a source of trouble for local law enforcement. Both Colloff and Morris suggest that arresting the husbands, and sticking with the theory supporting their guilt, helped defuse local tensions and made everyone in the community feel safer.
It’s natural for police and prosecutors to want to ease public fears. And it’s also natural for them to stick with the evidence that supported their preferred explanations. As University of Wisconsin clinical law professor Keith Findley shows in his excellent 2010 article Tunnel Vision, the phenomenon “is the product of a variety of cognitive distortions,” chief among them confirmation bias. In other words, we tend to give weight to evidence that confirms our existing beliefs. “Although such confirmation-biased information is often less probative than disconfirming information might be, people fail to recognize the weakness of the confirming feedback they receive or recall,” Findley writes. He cites studies finding that “police officers who are convinced that a suspect is lying are very resistant to changing their minds” and often “rate disconfirming or exonerating evidence as less reliable or credible than guilt-confirming evidence that supports their initial hypotheses.”
I called Brandon Garrett, the law professor who wrote the book on wrongful convictions and why they happen, and he pointed out that police and prosecutors have no obligation to pursue alternative explanations, or even to follow a particular method of investigation or keep a record explaining the course they’re taking. Which means it’s close to impossible to hold them accountable for their errors. Garrett pointed out that crime labs are different: They write down every step they take. “Even though they have crushing caseloads, they follow that procedure,” he said. And that means we know when there’s a broken link in the chain. Police too, Garrett thinks, should have to record every witness interview they do; perhaps they should also keep notes about how their thinking evolves or doesn’t. Garrett also suggested giving the defense more resources to do their own investigations or requiring police and prosecutors to open their files to the defense. Tunnel vision isn’t going away. But to protect the innocent, we should diminish its dark power.
Emily Bazelon is a Slate senior editor and writes about law, family, and kids. Her forthcoming book, Sticks and Stones: Defeating the Culture of Bullying and Rediscovering the Power of Empathy and Character. Find her at email@example.com or on Facebook or Twitter.