Study Shows Blood Pattern Analysis Is Just More Guesswork Posing As Scientific Evidence

from the blood-suckers dept

Another form of evidence used in criminal cases is being called into question. The latest (via CJ Ciaramella) to receive the dubious honor of being designated "dubious" is blood spatter analysis. This brings it in line with a long list of other things long-considered (and, in too many cases, still considered) to be evidence worthy of introducing into a court of law, joining bite mark analysis, hair analysis, um… pair of blue jeans analysis... and even the old standby, DNA analysis.

The problem with all of these sciences is that they're mostly subjective. Sure, they look pretty science-y. A lot of math and charts and lab coats and computers are scattered all over the place. Inscrutable printouts are carried by expert witnesses with years of experience under their belts. They show up in court and make claims about certainty of matches or probability of X contributing to Y, much of which can't be easily contested because, as mentioned earlier, the results are open to interpretation.

Despite this, a lot of what's called forensic science still ends up being used as evidence in criminal cases, even though it's more accurate to refer to it as forensic guesswork. Blood spatter analysis is no exception. This study [PDF] for Forensic Science International says the lack of solid standards in the blood pattern analysis field have resulted in experts looking at the same blood patterns but all seeing something different.

We investigated conclusions made by 75 practicing bloodstain pattern analysts on 192 bloodstain patterns selected to be broadly representative of operational casework, resulting in 33,005 responses to prompts and 1760 short text responses. Our results show that conclusions were often erroneous and often contradicted other analysts. On samples with known causes, 11.2% of responses were erroneous. The results show limited reproducibility of conclusions: 7.8% of responses contradicted other analysts.

That's a problem. How big of a problem is unknown. Actually, a lot about this is unknown. Differing opinions on blood spatter evidence can turn a suicide into a homicide or turn a killing from an act of self-defense to a murder. There's actual freedom riding on these interpretations, so it's crucial they be correct. And yet no one in the field (or in the court system) seems too concerned about ensuring this evidence is correctly analyzed.

Although BPA has been admissible as expert testimony for more than 150 years, the accuracy and reproducibility of conclusions by BPA analysts have never been rigorously assessed in a large-scale study.

In 2009, the National Research Council condemned blood pattern analysis as "more subjective than scientific." Nothing changed. In 2016, it called for testing of error rates in criminal forensic science. Again, nothing changed. Small studies were performed but nothing on the scale of this one, which involved 75 practicing blood pattern analysts and 192 samples. The results are far from encouraging. In fact, they point to enough of a margin of error that this sort of analysis should be prohibited from being introduced as evidence until standards are developed and put into practice that eliminates the subjectivity on display here.

But, given the 150 years of use and the minimum of interest in developing standards, this will also likely lead to nothing changing. What this research does do, at least, is give defendants something to use to challenge questionable evidence and questionable statements by prosecutors' expert witnesses.

Hide this

Thank you for reading this Techdirt post. With so many things competing for everyone’s attention these days, we really appreciate you giving us your time. We work hard every day to put quality content out there for our community.

Techdirt is one of the few remaining truly independent media outlets. We do not have a giant corporation behind us, and we rely heavily on our community to support us, in an age when advertisers are increasingly uninterested in sponsoring small, independent sites — especially a site like ours that is unwilling to pull punches in its reporting and analysis.

While other websites have resorted to paywalls, registration requirements, and increasingly annoying/intrusive advertising, we have always kept Techdirt open and available to anyone. But in order to continue doing so, we need your support. We offer a variety of ways for our readers to support us, from direct donations to special subscriptions and cool merchandise — and every little bit helps. Thank you.

–The Techdirt Team

Filed Under: blood pattern analysis, blood splatter analysis, evidence, junk science


Reader Comments

Subscribe: RSS

View by: Thread


  • icon
    mhajicek (profile), 21 Jun 2021 @ 11:06pm

    How big of a problem?

    Seems it is known. About a 10% error rate. Doesn't seem too bad, IF that error rate is known and acknowledged.

    reply to this | link to this | view in chronology ]

    • icon
      PaulT (profile), 21 Jun 2021 @ 11:12pm

      Re: How big of a problem?

      Yeah, the latter part seems to be the main problem. In some of these cases the science itself is complete garbage, but in other cases it's reasonably effective - but if the jury believe in the flawless CSI version of the science instead of the fallible real life version, some verdicts will be bad.

      reply to this | link to this | view in chronology ]

    • identicon
      Anonymous Coward, 22 Jun 2021 @ 2:48pm

      Re: How big of a problem?

      And what is the sigma there?

      The real problem is there are no standards, and there are way more than 75 BPA experts. The error rate from the study is both new and unacknowledged, and people will look at 10% like a 10% chance of rain and think "oh well certainly with 10% chance, there isn't an error" while still playing the lottery or going to Vegas. People are bad at this.

      And let's never mind the analyses which say whatever the cops and prosecutors hinted that they wanted them to say. That doesn't show up in a statistical test.

      reply to this | link to this | view in chronology ]

  • icon
    wereisjessicahyde (profile), 22 Jun 2021 @ 1:01am

    Hide Tim

    Dexter will be coming after you mate. You can't just go dissing his profession and expect to get away with it.

    reply to this | link to this | view in chronology ]

  • identicon
    BPA Guy, 22 Jun 2021 @ 4:47am

    I work in this field and you're not wrong. The field can't even agree on how to classify or name things. Can't do much science like that...

    It would be a lot more useful to look at various parts of the work (for any field in forensics actually) and say "this analysis is subjective" and "this analysis is objective". Both have their place, but they should be more clearly delineated - especially when presenting evidence.

    And IMHO, most of the work in BPA is subjective.

    reply to this | link to this | view in chronology ]

    • identicon
      Pixelation, 22 Jun 2021 @ 7:56am

      Re:

      "And IMHO, most of the work in BPA is subjective."

      This is the rub that prosecutors hate, and that is likely what keeps it from being expressed in the courtroom. Prosecutors care more about their record than they care about ruining people's lives.

      reply to this | link to this | view in chronology ]

  • identicon
    Anonymous Coward, 22 Jun 2021 @ 4:49am

    The problem with all of these sciences is that they're mostly subjective.

    As I've said before: There are two flavors of 'science': One is the fundamental belief that rational thinking is useful (Things like "the scientific method" are a direct outcropping of that).

    The other is a religious, fanatical at time, belief in the things said by people who are called (either by themselves or others) "scientist".

    reply to this | link to this | view in chronology ]

  • icon
    Bloof (profile), 22 Jun 2021 @ 4:54am

    It's fairly safe to say that if it's hyped up in TV cop shows, especially CSI, as the thing that can crack a case, it's probably bulls**t.

    reply to this | link to this | view in chronology ]

  • icon
    Upstream (profile), 22 Jun 2021 @ 5:46am

    Old, but still outrageous, news

    As the article points out:

    In 2009, the National Research Council condemned blood pattern analysis as "more subjective than scientific."

    And it was old news even then. Many people have been shouting this to anyone who will listen for several decades, probably most notably Radley Balko. But, as the article also points out, no one seems to be listening, especially not the criminal legal system.

    It is also worth noting that, with the exception of DNA testing, all of the forensic techniques in use by the criminal legal system were developed either by, or for, people associated with the prosecution side of that system, specifically for the purpose of helping the prosecution secure convictions. These forensic techniques were not developed for, and are not used for, ascertaining the truth.

    The accuracy, reliability, and evidentiary value of forensic evidence are almost always grossly overstated to juries, and many jurors have been heavily influenced by the CSI effect, which results in their giving grossly excessive weight to the evidentiary value of said forensic evidence.

    Correcting the situation will be very difficult, because, just as in the drug war, there has arisen a very large law enforcement / prison / industrial complex around the practice of this forensic hocus-pocus. That makes for a lot of powerful and influential people all trying to maintain the status quo.

    reply to this | link to this | view in chronology ]

    • identicon
      Whoever, 22 Jun 2021 @ 3:02pm

      Re: Old, but still outrageous, news

      It is also worth noting that, with the exception of DNA testing, all of the forensic techniques in use by the criminal legal system were developed either by, or for, people associated with the prosecution side of that system,

      I think that you will find that the initial development of DNA science in a criminal case was done by a team working with the police in the UK. Fortunately for the first person accused of the crime, the senior policeman in charge of the investigation followed through on the DNA analysis even though they had a suspect in custody: the DNA exonerated him. The culprit was eventually caught after someone reported overhearing a conversation in which someone told a friend that they gave a DNA sample for someone else (there was a mass DNA collection effort in the region of the country where the perpetrator was believed to live or work).

      reply to this | link to this | view in chronology ]

  • identicon
    Melvin Chudwaters, 22 Jun 2021 @ 7:22am

    Yet more proof that the forensic arts are difficult to master. This is why it's so important for prosecutors to only hire the most diligent of forensic artists, and for judges to disqualify the defense's posers.

    reply to this | link to this | view in chronology ]

  • identicon
    Anonmylous, 22 Jun 2021 @ 11:20am

    This is what happens when prosecutors and investigators turn a statistical tool into "hard evidence" because they can't come up with anything else. "Beyond reasonable doubt" is the bar, and tools like BPA should be used for eliminating suspects, not confirming them. Perhaps even going so far as to giving reason for a warrant to search further. But not for arrest and certainly not for prosecution. It was always a ballpark tool, as the amount of force someone who weighs 120lbs soaking wet and someone who weighs 240lbs dry as a bone, are in fact different, letting you eliminate suspects based on the physical ability needed to cause a specific impact.

    Prosecutors lead the charge in turning these tools into evidence rather than investigative leads. Police simply follow suit and this leads to lazy policework. Policework is difficult for a reason, our Constitution is geared towards making it so, as it should be. To prevent a tyrannical government.

    reply to this | link to this | view in chronology ]


Add Your Comment

Have a Techdirt Account? Sign in now. Want one? Register here



Subscribe to the Techdirt Daily newsletter




Comment Options:

  • Use markdown. Use plain text.
  • Remember name/email/url (set a cookie)

Close

Add A Reply

Have a Techdirt Account? Sign in now. Want one? Register here



Subscribe to the Techdirt Daily newsletter




Comment Options:

  • Use markdown. Use plain text.
  • Remember name/email/url (set a cookie)

Follow Techdirt
Special Affiliate Offer

Essential Reading
Techdirt Deals
Report this ad  |  Hide Techdirt ads
Techdirt Insider Chat

Warning: include(/home/beta6/deploy/itasca_20201215-3691-c395/includes/right_column/rc_promo_discord_chat.inc): failed to open stream: No such file or directory in /home/beta6/deploy/itasca_20201215-3691-c395/includes/right_column/rc_module_promo.inc on line 8

Warning: include(): Failed opening '/home/beta6/deploy/itasca_20201215-3691-c395/includes/right_column/rc_promo_discord_chat.inc' for inclusion (include_path='.:/usr/share/pear:/home/beta6/deploy/itasca_20201215-3691-c395:/home/beta6/deploy/itasca_20201215-3691-c395/..') in /home/beta6/deploy/itasca_20201215-3691-c395/includes/right_column/rc_module_promo.inc on line 8

Warning: include(/home/beta6/deploy/itasca_20201215-3691-c395/includes/right_column/rc_promo_jq_chat.inc): failed to open stream: No such file or directory in /home/beta6/deploy/itasca_20201215-3691-c395/includes/right_column/rc_module_promo.inc on line 8

Warning: include(): Failed opening '/home/beta6/deploy/itasca_20201215-3691-c395/includes/right_column/rc_promo_jq_chat.inc' for inclusion (include_path='.:/usr/share/pear:/home/beta6/deploy/itasca_20201215-3691-c395:/home/beta6/deploy/itasca_20201215-3691-c395/..') in /home/beta6/deploy/itasca_20201215-3691-c395/includes/right_column/rc_module_promo.inc on line 8
Recent Stories
.

This site, like most other sites on the web, uses cookies. For more information, see our privacy policy. Got it
Close

Email This

This feature is only available to registered users. Register or sign in to use it.