Murphy's Law of Investigation

 Posted on December 12, 2008 in Uncategorized

From today's Houston Chronicle:

DNA evidence - collected in 2002, but unexamined until now - has cleared [RR,] a Houston man serving a 40-year prison sentence for the sexual assault of a child.

The complainant (the Chronicle calls him "the victim", but in this case that term is ambiguous) who identified RR had, when describing his assailant, not mentioned RR's very conspicuous facial disfigurement, caused by a shotgun blast years before.

RR's case brought to mind Murphy's Law of Investigation:

Enough investigation will tend to support your theory.

I cribbed that from Murphy's Law of Research ("Enough research will tend to support your theory"). The principle behind Murphy's Laws of Research and Investigation is confirmation bias, the human tendency to seek out and recognize the data that support their preconceptions, and to avoid data that challenge those preconceptions.

Could confirmation bias have contributed to RR's conviction? It's often the case that a prosecutor will have made up her mind about an accused's factual guilt before even reading the offense report; the prosecutor in RR's case was not interviewed for the Chronicle article, but could that have happened here?

Might a prosecutor who hadn't already decided that RR was the right guy have been more diligent in looking for evidence? Might such a prosecutor have discovered in 2002 that there was a rape kit, with DNA to try to match against RR's?

Might RR, as a result, have spent the last six years a free man?

The prosecutor may have counted on the defense lawyer to run down all of the possible exculpatory leads. But sometimes lawyers forget that often cops and prosecutors get the wrong guy. Can you imagine a defense lawyer sharing the prosecutor's preconception that RR was factually guilty? Could confirmation bias have lead such a defense lawyer not to go to the trouble to find out whether the DNA recovered from the complainant matched RR's?

Which brings us to this, from Dallas criminal-defense lawyer (and ex-prosecutor) Robert Guest:

When I was a DA I had professional state witnesses (cops, intox experts) and my own team of investigators. There was also the feeling that the appellate courts worked to benefit the State and uphold convictions. Defense experts and theories were largely mocked and dismissed at my training seminars. Only as a defense attorney did I learn why and how field sobriety testing is flawed, what the limitations of intoxilyzer machines were etc.

That's confirmation bias at work: Robert didn't, as a prosecutor, learn why and how field sobriety testing was flawed because his job was to prosecute people, and finding reasons to challenge his own evidence didn't help him do that job.

We all have preconceptions and prejudices formed by our life experiences. Any of us might unknowingly suffer from confirmation bias that helps us maintain these preconceptions, even if they're wrong. A prosecutor might rightfully assume that a person accused of a crime committed that crime because - let's face it - the cops usually get things right, and in the small percentage of cases in which the wrong guy is arrested there's a defense lawyer who will fight zealously to prevent an injustice.

But, no matter how jaded, a defense lawyer can't assume that the cops got it right because - let's face it - the cops often don't get things right, and in those cases the defense lawyer had better not be prevented, by confirmation bias or anything else, from seeking out the evidence that might save the accused from prison or death.

It bugs me a bit when (rarely) clients ask whether I believe they are innocent. It doesn't matter to me, and I haven't made up my mind. Besides, I think the question is a sign of a guilty conscience; when I'm trying to defend someone I don't need him presenting me with evidence of his guilt (confirmation bias!).

But you can see how it would benefit the accused for his lawyer not to come to the job with the preconception that the accused committed the crime of which he was accused.

(It is, incidentally, suboptimal for the criminal-defense lawyer to uncritically decide that the accused didn't do the deed, because that might - confirmation bias again - get in the way of his red teaming the case.)

Share this post:
Back to Top