Confessions Corrupt Eyewitnesses

People confess to crimes they don't commit. They do it a lot. What's interesting about this research is that confessions—whether false or true—corrupt other eyewitnesses:

Abstract

A confession is potent evidence, persuasive to judges and juries. Is it possible that a confession can also affect other evidence? The present study tested the hypothesis that a confession will alter eyewitnesses' identification decisions. Two days after witnessing a staged theft and making an identification decision from a lineup that did not include the thief, participants were told that certain lineup members had confessed or denied guilt during a subsequent interrogation. Among those participants who had made a selection but were told that another lineup member confessed, 61% changed their identifications. Among those participants who had not made an identification, 50% went on to select the confessor when his identity was known. These findings challenge the presumption in law that different forms of evidence are independent and suggest an important overlooked mechanism by which innocent confessors are wrongfully convicted: Potentially exculpatory evidence is corrupted by a confession itself.

More:

When asked to explain their change, subjects revealed they were actually convinced by the confessor, and not simply complying with it, saying, "His face now looks more familiar than the one I chose before."

Posted on February 4, 2009 at 6:35 AM • 17 Comments

Comments

CalumFebruary 4, 2009 7:36 AM

Is this not fairly common knowledge? The one time I picked someone out of a line-up, I was quarantined throughout my visit from meeting any officers who had had any dealings with the accused, for this exact reason.

Edward the ConfuserFebruary 4, 2009 8:42 AM

In an experiment people are shown pairs of photos and asked to pick the one they prefer. Then they are sometimes asked for a reason for picking this photo over that one. They succeed in rationalising a choice even when given the wrong photo from the pair. (Described IIRC in Dan Gilbert's "Stumbling on Happiness".)

sooth sayerFebruary 4, 2009 8:56 AM

This is tainting a witness - I am surprised at the low % of acceptance; which shows something totally contrary to the conclusions drawn - that the witnesses tend to trust their eyes even when told to the contrary.

Bogus science torturing data to make a bogus point.

billswiftFebruary 4, 2009 10:00 AM

Anything and everything "corrupts" or contaminates eyewitnesses. See Elizabeth Loftus's "Witness for the Defense" for multiple real world examples.

Bryan FeirFebruary 4, 2009 10:10 AM

Reminds me of a comment I heard a while ago, and wish I could remember the source of. It was something along the lines of:

"Anybody who says there are two sides to any story has never tried to interview three eyewitnesses to the same accident."

Clive RobinsonFebruary 4, 2009 11:02 AM

@ Bryan Feir,

"Anybody who says there are two sides to any story has never tried to interview three eyewitnesses to the same accident."

For the simple reason of perspective.

Simple example put four people at the corners of a square and bounce a ball in. Then ask them which way it bounced you will get four answers that are different but it is unlikley the real answer will be given unless the ball bounced directly towards or away from a witness. So under most circumstances there will be n aproximations to the real answer where n is the number of witnesses.

Then make the situation more complex and you can understand why even those n statments will be wildly different.

crackFebruary 4, 2009 11:06 AM

This isn't applicable just in a tainted witness case, it is applicable when a witness who isn't used for a lineup is subsequently called to the stand. Not all eye witnesses will go through a lineup, and even if they do if they are eventually called to court it's likely they will have heard of a confession and had that change their perception of events.

Clive RobinsonFebruary 4, 2009 11:16 AM

Most studies I have read indicate that an eye witness identification is only reliable when the witness knows the perpetrator.

Various studies have shown that simple questioning about height etc can make a witness belive the person they saw was a different height. Showing people "mug shoots" in certain ways tends to make a witness morph their memory towards the photos. And of course something as simple as, rumpled hair and clothing, being unshaven or having noticably different cloths (work cloths to suit etc) can be used to make a suspect stand out from the line up.

The police then tell their favourd suspect they have been positivly identified and with a little sugestion about coping a plea etc a false confession would not be difficult to obtain from many personality types.

A lot of studies have sugested that after 24hours there is less than a 25% chance the witness will correctly identify the perp will when the correct line up precautions are taken.

So the question is why do courts and juries take so much notice of ID line ups results and confessions...

I guess it's because it makes things easy for them...

And with plea barganing I'm surprised we don't hear about more cases of false prosecution.

fatalistic frogFebruary 4, 2009 11:26 PM

Why you should never talk to the police.
An attorney and a cop explain to a group of law students.

http://www.chycho.com/?q=node/2188

No degree of lily-white innocence can protect you from the vulnerabilities created by even truthful statements that can be brought before a court.

RogerFebruary 5, 2009 1:13 AM

The fact that witness recollection can be very unreliable is well known -- and one of the reasons we rely more and more on cameras...

Among other things, it is not uncommon for a suspect to be captured or otherwise located weeks, months or even years after the event. Witness reliability fades rapidly with time, whereas properly stored photographs are effectively permanent.

There are, of course, already detailed procedures required for a lineup that are intended to prevent this form of witness contamination, and many others beside. In particular the witness is not allowed to talk to any person who knows who the suspect it.

Having said that, it is not only possible but fairly easy to train a person to do much better than average at accurate recall of faces.

BF SkinnerFebruary 5, 2009 6:48 AM

And yet another reason why the tribunal method in GITMO is fundamentally flawed. If an accused cannot challenge witness statements made against them we might as well just go with "well he looks guilty. Hang him."

billlFebruary 5, 2009 7:02 AM

@ roger
'witness.. unreliable .. and one of the reasons we rely more on ... cameras'

- Photoshop?
- Cameras that are mysteriously offline when UK police shoot innocent foreigners (c.f. Jean Charles De Mendes)
- Privacy problems?

;)

FBFebruary 5, 2009 9:52 AM

The main problem of our system is that the justice look for one guilty and not the truth. As soon as some one confesses they convict him. Everyone is then happy. The victim feel safe again, the police have a good number of crime solved. The society feel also good because it didn't cost that much to solve this crime.

SSFebruary 6, 2009 11:35 AM

Privacy problems, photoshopping and all such technological troubles aside, it is widely known that the testimony of live human beings are often - very often - biased in one way or another. And if it isn't, it's been compromised in some way, often - very often - without the knowledge of the witness itself.
A confession, a remark, something viewed in the newspaper or seen on TV can be enough to make a witness "remember" something new, or amend something old.
Like Calum said in the first comment, this is fairly widely known.

Leave a comment

Allowed HTML: <a href="URL"> • <em> <cite> <i> • <strong> <b> • <sub> <sup> • <ul> <ol> <li> • <blockquote> <pre>

Photo of Bruce Schneier by Per Ervland.

Schneier on Security is a personal website. Opinions expressed are not necessarily those of Co3 Systems, Inc..