To catch a thief and fool a scientist

If you only listen to one radio programme this month, make it this one. The BBC Radio 4 programme Fingerprints on Trial explores how identifying people at crime scenes by their prints is subject to serious psychological biases and is not the exact science that we, and ironically, the forensic fingerprint community, like to believe.

It covers some spectacular high-profile cases, the science behind how prior knowledge can bias the supposedly objective identification of prints, and the baffling fingers-in-the-ears lalalala response of some fingerprint experts who just completely deny it’s a problem.

The programme riffs on the work of psychologist Itel Dror who has shown that changing the ‘backstory’ to a case can alter what fingerprint matches experts find.

So here’s how these biases could work in practice. Fingerprint examiners in this country [the UK] generally know the type of crime their working on. Any murder is high profile, so the chances are they’d know quite a bit about the case. They might see crime scene photographs and might even have heard snippets from detectives working on the case. And then when they start to check the fingerprints from the murder scene, evidence from cognitive psychology shows that what they know, or think they know, can influence what they then see in the prints.

Combines gripping sad-but-true whodunits, cutting edge cognitive science and a pressing issues for forensic science.

Excellent stuff.
 

Link to BBC streamed version and programme info.
mp3 of podcast from BBC.

5 Comments

  1. Emmy
    Posted March 18, 2011 at 12:32 am | Permalink

    Sounds like a great show on BBC. And pardon my ignorance but aren’t fingerprints matched through a computer program? If not I think it would be a pretty good argument for a “blind” forensics examiner method.

    • Posted March 18, 2011 at 8:18 am | Permalink

      “…aren’t fingerprints matched through a computer program?”

      Fingerprints are screeed with AFIS which reduces the potential number of prints that may match. The fingerprint examiner matches one of these prints. (This is covered in the report).

      A strange difference in validity of screening assays is accepted by society between searching for disease and searching for criminal behaviour. I think the reason is due to an Us and Them attitude. Screening for diseases such as cancer are to be applied to Us and so most be robust, ie, they must have false positive and false negative rates as well as the initial background incidence rates. Criminal screenings (fingerprints / sniffer dogs) are for them, criminals who are certainly not one of us; therefore the assay can be based upon ignorance and myth.

      Pathetic isn’t it?

  2. Steve Merrick
    Posted March 18, 2011 at 4:05 pm | Permalink

    It’s surprising how few people know (or accept) that we generally perceive what we expect to perceive.

  3. Paul
    Posted March 18, 2011 at 7:56 pm | Permalink

    Excellent program, nice find. I’m shocked after hearing the AFIS procedure that this was not obviously open to bias. It appears to be a very flawed procedure. I wonder how many poor souls lost their liberty due to errors? Truly eye opening.

  4. Posted March 28, 2011 at 5:04 am | Permalink

    In America, to convict it, has to be beyond a shadow of a doubt. This does cast a shadow of doubt on relying on this.


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