Forensic science

Study on Bloodstain Pattern Analysis Finds 'Conclusions Were Often Erroneous'

Bloodstain pattern analysis is one of several forensic techniques that has come under scrutiny in recent years for its lack of established error rates.


The largest-ever black-box study on the accuracy of bloodstain pattern analysis (BPA), a widely used forensic technique, has found concerning error rates and disagreement among analysts.

The study, published in the August 2021 volume of Forensic Science International, is the most rigorous attempt so far to measure the accuracy and reproducibility of BPA, in which analysts interpret bloodstains at crime scenes.

"Our results show that conclusions were often erroneous and often contradicted other analysts," the report found. "Both semantic differences and contradictory interpretations contributed to errors and disagreements, which could have serious implications if they occurred in casework."

For the study, researchers collected 192 examples of blood spatters from controlled samples and actual casework and presented pictures of them to 75 practicing BPA analysts for classification.

"On samples with known causes, 11.2 percent of responses were erroneous," the study found. "The results show limited reproducibility of conclusions: 7.8 percent of responses contradicted other analysts."

BPA is one of several forensic disciplines that has come under increased scrutiny over the last decade, along with other methods—such as bite mark, hair, and shoe print analysis—that do not have established error rates and rely on pattern matching or subjective interpretation. Yet they are widely accepted in courtrooms across the country, despite concerns over reliability and a number of wrongful convictions.

In 2018, ProPublica published a series of investigative stories on the history and use of BPA. It found a disturbing amount of questionable casework, exonerations, and investigators with no more than 40 hours of BPA training testifying in court. (For the story, the reporter herself went through a 40-hour class on BPA.) It also noted that there were few scientific studies on the reliability of the methods.

A 2009 National Academy of Sciences study was, at the time, the most extensive done in the U.S. on the scientific validity of several commonly used forensic techniques, and it was critical of blood spatter analysis.

"In general, the opinions of bloodstain pattern analysis are more subjective than scientific," the study said. "Extra care must be given to the way in which the analyses are presented in court. The uncertainties associated with bloodstain pattern analysis are enormous."

The Justice Department came under pressure to improve forensic standards after the FBI admitted in 2015 that two dozen examiners in one of its hair analysis labs had given flawed testimony in hundreds of cases. In those cases, 32 defendants were sentenced to death; 14 were eventually executed or died in prison.

A 2016 report by the President's Council of Advisors on Science and Technology (PCAST) found that reviews of several commonly used forensic methods "have revealed a dismaying frequency of instances of use of forensic evidence that do not pass an objective test of scientific validity."

In the case of bite mark evidence, for example, the report stated that "available scientific evidence strongly suggests that examiners not only cannot identify the source of bite mark with reasonable accuracy, they cannot even consistently agree on whether an injury is a human bite mark."

However, both the Obama and Trump administrations resisted calls to improve forensic standards. The Obama Justice Department rejected PCAST's recommendations to require expert witnesses to disclose error rates in their testimony and, where methods haven't been scientifically verified, not use them at all. 

In 2017, Attorney General Jeff Sessions disbanded the National Commission on Forensic Science, an independent panel of scientists, law enforcement, judges, and defense attorneys created by the Obama administration in 2013 to review the reliability of forensic science used in trials.

The authors of the most recent study on BPA noted that it differed from actual casework, where analysts have additional context from the crime scene, and that the majority of respondents almost always arrived at the correct conclusions, suggesting multiple independent verifications may help. However, the authors recommend standardizing BPA methodology and terminology to reduce contradictory interpretations.

"Although the error and reproducibility rates measured here should not be taken to be precise measures of operational error rates," the study said, "their magnitude and the fact that they corroborate the rates measured in previous studies, should raise concerns in the BPA community."

They should raise concerns for defendants, too.

The study was conducted by researchers at the private Virginia-based firm Noblis, the Kansas City Police Department Crime Laboratory, and Indiana University.

NEXT: When Is a Civil Forfeiture Based on Drug Offenses Excessive? Always.

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39 responses to “Study on Bloodstain Pattern Analysis Finds 'Conclusions Were Often Erroneous'

  1. The blood stains show that everyone is guilty and the Gov is allowed to take all of your stuff.
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    2. The blood stains show that everyone is guilty and the Gov is allowed to take all of your stuff.This dog say down which means the Gov is allowed to take all of your stuff..more detail………….CLICK HERE.

    3. No accountability for cops who convict innocent people.
      No accountability for prosecutors who convict innocent people.
      No accountability for fake scientists who convict innocent people.
      Looks like another pattern.

  2. On samples with known causes, 11.2 percent of responses were erroneous

    88% is a passing grade in any discipline.

    1. 88% error is enough for reasonable doubt.
      The standard in court is not a school grade standard for a reason

      1. 88% errors would certainly be a problem, but in fact it’s 11% errors.

        1. My bad, mistyped, 11% is still reasonable doubt

          1. By itself. But place it in tandem with other evidence.

            But apparently we’re to disregard any evidence unless it is conclusive by itself?

            1. That’s the way our critical thinking world is going.

        2. Also, while IANAL, I’m pretty sure no one has ever presented a “See? Blood stains. I rest my case.” before the court.

    2. If our structural engineers were wrong 11% – 12% of the time, watch out. One in 8.5 buildings is in danger of collapse.

      1. Engineers were frequently wrong until enough trial and error tightened our error rates. How many rockets do you suppose exploded before our first launch? How many bridges collapsed? There used to be the engineer had to walk out onto their structure to test it. If they died, good riddance to a bad engineer.

        Should we abandon BSA because it is a relatively new discipline? Has the error rate decreased? And since when is debate a problem? Isn’t that the nature of science?

    3. It is frequently presented in court as much closer to 100%. That’s a problem.

  3. The only subset of forensic evidence that could pass a Daubert hearing, is DNA fingerprinting. And they still fuck that up:

    1. The rest of it, so I am told, is useful for bamboozling juries, or for convincing defendants to confess or plead to something else. Alternately, enough independent pieces of physical evidence can stack themselves up in a Bayesian manner, that we can say, ‘Yeah, he did it beyond a reasonable doubt.’ 10 point fingerprint match + bullet retrieved from victim that is same caliber, rifling pattern, as gun the defendant possessed + footprints + defendant’s cell phone pinged towers near site of murder at time of murder, etc…

      It’s a good thing most crooks are dumb, and think they can out-talk someone who questions criminal suspects as their job.

      1. Similarly, saying someone was wrongly convicted means somebody potentially committed a crime in convicting them I’m having trouble thinking of how an 11% error in bloodspatter analysis alone leads to an exoneration. “We calculated that there was 4L of blood on the floor when really there was only 3.6L so it’s possible no murder took place.” I’m not saying it doesn’t happen, just the obvious explanations that come to mind all sound absurdly contrived. I’d want something more than just “The blood spatter analsysis was wrong.” to say anything other than a mistake occurred.

    2. Bullshit. That useless DNA shit can’t even tell us if the sample came from a male or female anymore.

      1. The evidence says what Kamal says it says

      2. That useless DNA shit can’t even tell us if the sample came from a male man or female woman anymore.

        Learn to Science bigot.

  4. So it’s almost 90% accurate which you describe as “often erroneous” and hide the real numbers until the 5th paragraph. Have you combined your editing department with MSNBC?

  5. I have it on good authority, from a close personal friend, that blood spatter analysis is every bit as accurate and reliable as drug dogs, field drug tests, officers detecting a faint smell of marijuana, and confidential informants.

    1. And gut feelings…and no-knock raids…

  6. Good timing as I was reading up elsewhere on the subject. Forensics is being exposed as much less accurate than so called experts portray it, even common fingerprinting.

    The only field with a strong track record of accuracy is DNA and even that can be affected by bad chain of custody, lab contamination, lab errors and purposeful falsification (planting DNA evidence)…

    1. Hazy recollection- it was a newsletter from the Georgia Bar association citing a (then) recent federal ruling about forensic evidence, and inviting defense attorneys to call upon their own experts in the analysis.

      The short was this judge was not going to necessarily accept proclamations from the prosecution as definitive.

      This is probably the best that can be hoped for (providing the defense has the funds to call on their own experts).

      In any case, the scientism of forensic evidence is starting to crack. Too bad it left a trail of bodies in its wake.

  7. But Dexter always got the right guy with his BPA….

    1. Dexter’s super power was to have people completely change their behavior for no reason, when it would benifite dexter

    2. Then chopped them up and threw the body parts in the ocean.

      Colombo always brought up the ‘boys in the lab’.

      “One more thing. I checked with the boys in the lab. They said this cigar butt was purely American tobacco. Mr. Greene was very particular about his cigars. He only smoked a Havana brand he had shipped in”

      “So how did this cigar get into his ashtray the night of the murder right next to his favorite brand. There were two cigar butts in that ashtray. I checked with the maid. She cleaned that out every morning”.

      I always suspected that the ‘boys in the lab’ was a ruse. He never relied on that to catch the murderer.

  8. BPA is one of several forensic disciplines that has come under increased scrutiny over the last decade

    And there have been a few people trying to raise the alarm over this pseudo-scientific nonsense for about 40 years.

  9. People think forensic science is awesome because that’s how it’s portrayed on tv. In real life it’s just people getting paid by the police to say whatever it takes secure convictions.

  10. Stay at home mom Kelly Richards from New York after resigning from her full time job managed to average from $6000-$8000 a month from freelancing at home…

    This is how she done it…

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  12. We could have used a simple summary of what it meant to be right or wrong. What’s the other way of answering the BPA analysis answers and how good is that. 88%, 7%, these numbers don’t have handles.

    1. Ignoring the IDK known classifications and the IDK evaluator responses, we get a sensitivity of 78%, specificity of 88%. .For making predictions about the future to make decisions about investor money, that’s great. (Those values are sim to what a FICO or Vantage score provides.) For evaluating facts on the ground to make decisions in criminal court, unacceptable.

  13. Forensic science is not science. It was created for police by police. Crime labs are ran by police, sheriff’s and prosecutors. They give biased information when submitting evidence that greatly affects the labs objective. This includes DNA interpretation they do not do DNA sequencing. Although DNA was founded in science, the criminal justice system has twisted it to fit their needs. Labs do not submit error rates for DNA either they misstate the statistics most don’t understand the basis of the statistics. There is no national standards or oversight it’s an absolute disaster and it’s easy to target the poor who can’t afford a defense, this leads to innocent people taking pleas and innocent people getting convicted.

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