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Forensic Failure

Testimonial power is the power we have to determine the opinion of others by testifying. To testify is to make sincere assertions in such circumstances under which we are understood to be offering those assertions as to be worth relying upon. When things go well, we tell people what we know and they come to know it through our telling them. We all have varying degrees of testimonial power relative to subject matter, to circumstance, to our knowledge and to what we are known by others to know.


Forensic experts are granted immense testimonial power. Their testimony is taken to be sufficient for conviction in the absence of any other evidence. Judges are reluctant to delve into the grounds of their expertise or into underlying disagreements among experts on the meaning of forensic evidence or the basis of interpretation. Their claims are taken to be backed by the epistemic authority of scientific method.


I do not think that forensic experts presently warrant the testimonial power they have been granted.

Forensic experts are under the most stringent epistemic duties because of the testimonial power they have. We have seen kinds of forensic failure that could not occur were the forensic experts adhering to their epistemic duties. 

 The problem here is not fallibility. Inevitably experts get it wrong some of the time and we cannot expect forensic experts to be infallible. However, there are kinds of failure which casts doubt on the right to testimonial power, either of individuals or of an entire profession. In the case of the forensic profession all of the following flaws are of that kind
• bias in favour of giving the police what they want
• biased  interpretation of evidence due to contamination by irrelevant information provided by the police
• unchecked, untested  and untestable claims of indicators
• dogmatism, especially about the reliability or significance of certain kinds of evidence
• ignorance of statistics
• persistent failure to discipline or remove proven inadequate experts
• charlatanry

Recently one of the most appalling cases of such failings has again come to light. A dentist called John Piakis has been proved to have fabricated bite mark evidence—in one case by ‘jamming Duncan’s dental mould into the body of the young girl Duncan was accused of killing’(here ). I said come to light again because this dentist has been exposed on a number of occasions, as early as 2001, and yet the courts have continued to rely on his evidence.

Such a failure casts doubt on the entire forensics profession. In constitutes an example of almost all the flaws I listed above. This could not happen if the profession were attending to its epistemic duties. On the very first occasion that he was identified as a charlatan the profession should have excluded him.

Yet worse: the National Academy of Sciences recently concluded that there is ‘no evidence of an existing scientific basis for identifying an individual to the exclusion of all others’ using bite mark analysis (here ). That is extremely shocking. It means that bite mark evidence has been used in court for very many years despite the fact that its reliability had not been empirically confirmed—indeed, had barely been checked. Any yet the very basis for the testimonial power we have granted forensic experts is supposed to be their use of scientific method. How can we possibly rely on the testimony of a profession that it is now clear simply makes stuff up without bothering to verify whether what they made up really is an indicator? Yes, identification by bite mark seems intutively plausible, but so does the sun going round the earth. Scientists are supposed to take the next step.

Consequently, until the forensics profession gets its house in order none of us should grant them the influence on our opinion that they have hitherto been granted. Most importantly, the courts must abandon deference to forensic experts and institute more critical appraisal during trials, including allowing questioning of the empirical basis and interpretative methodology on which forensic experts make their claims.

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2 Comment on this post

  1. Is there an acceptance of shaky expert testimony for the same reason that police are usually believed in their accounts at trial, however unbelievable they may be to a detached observer, because of the bureaucratic desire to complete and close files? The judge and the policeman are, after all, bureaucrats. I’m not sure about the average juror.

  2. Nicholas Shackel

    Yes, a full explanation of how it goes in court would include things like the considerations of the efficient administration of justice and the self interest of the participants. These can all be distorting pressures. My concern, however, is solely with the question of how much testimonial power is warranted. One of the problems is that expert testimony is precisely testimony whose shakiness or otherwise is *not* evident to a non-expert detached observer.

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