Undermining a Bloodstain Pattern Analysis

When it comes to the presentation of evidence in a legal setting, it can be tempting to assume that all scientific reports are impartial and accurate.

Yet when it comes to establishing truth from error, reality from speculation, bloodstain pattern analysis can obfuscate, rather than clarify.

While bloodstain pattern analysis has been widely accepted by various appellate courts, there has actually been very little proof of its accuracy.

In fact, the uncertainties of bloodstain pattern analysis have been described by the National Academy of Sciences as “enormous,” with the field itself accused of being “more subjective than scientific.”

When handling the challenges of a false child abuse allegation, it is vital to understand what is being presented, particularly when the “irrefutable” science may not be all that accurate.

The principle of bloodstain pattern analysis is based on an understanding of how blood typically behaves and extrapolating from that how the blood at a crime scene came to be there.

It cannot be denied that the pattern left by a bloodstain - from the size, location, and distribution - can provide useful information.

However, the methodology of bloodstain pattern analysis can show only the “what,” and not the “who” or even necessarily the “how.” While it is often suggested that bloodstain pattern analysis is comparable to DNA evidence, the field of study originated outside of a scientific environment and has had very little oversight.

Blood spatter analysis has been accused of ignoring the way that blood responds once it has left the body and failing to account for the varying contexts in which blood can be present in a location.

Furthermore, analysts also work with very generalized models that do not provide irrefutable evidence.

While different police departments may have their own bloodstain pattern analysts, typically these professionals have a background in math or physical science.

This becomes problematic when we factor in the amount of training an individual will undergo. The International Association for Identification (IAI) offers certification. However, this is optional rather than mandatory.

Throughout the course of exploring a case, an analyst will also be exposed to a huge range of information. From working with investigators, and processing witness statements, and particularly in cases with children, the analyst may find themselves exposed - even subconsciously - to information that influences their interpretation.

When it comes to providing expert testimony, as well as filing bloodstain pattern reports, there is also evidence that some analysts will over-represent their findings. It is vital to check a report to ensure that the evidence presented is scientifically substantiated.

This can be successfully challenged with careful questioning. In trial testimony in Phoenix, AZ, one bloodstain pattern analysis misrepresented their experience by stating, “I’ve been through probably 300 hours of investigative school in which blood spatter analysis was probably 10 percent.” While on the surface this might seem impressive, 30 hours of training is still well below that of even a Basic Bloodstain Pattern Analysis Course.

In fact, examining the language of a bloodstain pattern analysis is an excellent way to assess the weight and value of the analysis.

Phrases such as “more likely” or “tend to” indicate that the subsequent claims lack the necessary scientific rigor. The same can be said when a report speculates or makes assumptions or states “facts” with any degree of certainty.

For example, “The cast-off pattern showed the assailant was right-handed” may be a statement that falls outside of the bloodstain pattern analyst’s role, responsibility or even knowledge.

Likewise, the presence of emotive language, biased language, or oversimplification of the case can indicate unsubstantiated opinions. It is integral to the notion of a bloodstain pattern analysis that the language of the report focuses exclusively on objective facts, not opinions.

Bloodstain pattern analysis is a forensic tool that can be used to help provide a better understanding of what may or may not have occurred, but it is by no means exact. According to one report, in various scenarios, the degree of inaccuracy can be as high as 59%.

The same report also indicates that if the patterns a bloodstain analyst looks for have been interrupted, it can become decidedly unclear as to both the cause and the timeline of events.

If the government uses a bloodstain analyst report in its case against you, just know there may be ways to attack it.