A home security video surveillance system captured relevant events that transpired outside the home before and after two murders were committed nearby. Of note, it recorded images of a person walking and carrying what appeared to be a shotgun. The facial features and race of the person of interest were not discernible due to reduced image quality caused by darkness and distance from the camera. What was of interest to the police was if the height of this person could be determined.
The Reverse Projection Process
The FBI Forensic Audio, Video and Image Analysis Unit was asked to assist local police for the purpose of height determination. The FBI expert assigned to the case analyzed the home surveillance video images to determine which image was most conducive to photogrammetry analysis and was able to locate a suitable image. That image became the questioned image in her analysis. The expert located and confirmed the identification of the same camera that recorded the questioned image. She viewed live footage from the camera so that she could align the camera to the same position as when it recorded the questioned image. She then placed a height chart in the same spot where the person of interest had been standing. She also stood in the same position as the person of interest. Images were recorded using the original surveillance system and overlays were examined as between the expert’s position and the person of interest’s position to confirm that they were both standing in the same location.
The expert then created an overlay of the questioned image and the height chart to measure the height of the person of interest. She superimposed a yellow arrow at the top of the headwear of the person of interest and determined that height to be 5’8”. The expert undertook further measurements to ascertain the margin of error in her height assessment based upon image resolution and the positional accuracy of the height chart. The result was an opinion that the person of interest, measured from the ground to the top of their headwear, was 5’8” plus or minus two-thirds of an inch.
The expert had also recorded her height in relation to the height chart and the person of interest. This assisted her because her height was a known value. She opined that her height estimate of the person of interest was within a reasonable degree of scientific certainty. She was never told the height of the suspect (the person of interest). In her report and in her testimony, the expert stated that “the degree of uncertainty in this measurement could be significantly greater” based on several variables, including “the subject to camera distance, the resolution of the imagery, the unevenness of the landscape, and the body position of the subject.” She said that she does not have a scientific way of quantifying those further factors and how they might impact her height assessment and reported them out of an abundance of caution.
The Legal Challenge
In a pre-trial motion, the defence sought to have the expert’s evidence excluded on the basis that the measurement uncertainty should preclude it from being presented to the jury. The defence presented their own expert in photogrammetry. While the defence expert did not quarrel with the questioned image selected by the FBI expert for her measurements, he disagreed with her opinion on height and margin of error. He stated that other factors made the selected image unsuitable for analysis, including whether the top of the headwear and footwear location could be determined, and the unevenness of the landscape. The trial court denied the motion on the basis that the margin of error is a question of weight to be evaluated by the jury and the state was therefore permitted to present the expert evidence at trial.
At trial, the FBI expert confirmed in cross examination that she could not determine what type of headwear the person of interest was wearing, whether it worn high on the head or low to the scalp, or whether footwear added height. The defendant was convicted of two counts of murder and other counts. The Court of Special Appeals (an intermediate appellate court) reversed the conviction on the basis that the trial court erred in admitting the expert testimony. It found that the inability of the expert to provide a margin of error for the additional variables noted by her rendered the height determination unreliable and therefore inadmissible. The Court found there to be an analytical gap between the available data and the expert’s opinion. The state petitioned the Court of Appeals to review this ruling.
The Second Appeal
In State of Maryland v. Matthews, 479 Md. 278, 277 A.3d 991 (2022, Court of Appeals of Maryland), the Court undertook an extensive analysis of the impact of margin of error on the scientific validity and reliability of an expert’s measurement opinion. Following an extensive review of the facts and the law pertaining to the admissibility of expert opinion evidence, the Court found that the methodology used by the expert was reliable. Neither party took issue with this aspect of the expert evidence. The Court further found that the unknown degree of uncertainty concerning the height determination was a question of weight for the jury to consider, not a question of admissibility.
The Court distinguished between measurement uncertainty arising from the methodology used and uncertainly at the conclusion stage. Uncertainty that is inherent in the methodology is treated differently than reliable methodology that produces uncertain results. If the uncertainty arises at the conclusion stage, as it did in this case, the court must determine whether the uncertainty is the product of an analytical gap in the analysis and whether the uncertainty renders the opinion unhelpful to the trier of fact. In this regard, the Court stated:
“Matthews fails to appreciate the distinction between uncertainty inherent in an expert’s methodology and uncertainty that applies to an expert’s conclusions following the application of a reliable methodology. If an unacceptably high margin of error exists whenever a particular scientific technique is applied or no error rate can ever be determined with respect to that technique, a trial court may well decide to exclude testimony concerning the application of such a technique. In that situation, the court is concerned about the inherent unreliability of the expert’s methodology, i.e., the unacceptably high risk of an inaccurate conclusion being reached in every case where the technique is used. A different situation applies where an expert applies a reliable technique to an adequate supply of data, but in reporting her results, states that she is unable to quantify a specific degree of uncertainty/margin of error. That scenario is generally less problematic than where an expert has applied a technique that is unreliable in every instance in which it is used.”
Trial courts should be most concerned about the reliability of the methodology used by the expert. If the methodology is sound, the evidence should not be excluded merely because the conclusion may be inaccurate. Such conclusions should only be excluded if they amount to “mere speculation or conjecture”. An analytical gap is caused by “the failure of the expert witness to bridge the gap between his or her opinion and the empirical foundation on which the opinion was derived.” In this case, there was no analytical gap – that is, there was no disconnect between the result of the reverse projection photogrammetry and the expert’s opinion. The uncertainty in the final opinion which considered the noted variables did not detract from the admissibility of the opinion, only its weight. The probative value of the opinion was a matter for the trier of fact to decide.
Analysis
This is a helpful decision because it parses out the distinction between unreliable methodology and uncertain results. Experts in areas such as bite mark analysis, Shaken Baby Syndrome, gait analysis, and others face challenges based on the alleged unreliability of the methodology used. If unreliability is proven to exist, then the evidence should be ruled inadmissible as it would be of little or no probative value. If the methodology is proven to be sound, then the results would generally be admissible, and any measurement or opinion uncertainly would be a question of weight for the trier of fact to consider.