Fingerprint Experts Question Fingerprint Science

Fingerprint Expert’s Testimony Held Insufficient to Support Conviction

Written on Saturday, August 15th, 2020 by T.C. Kelly
Filed under: Expert Opinions, General, Working with Experts

Drawing a distinction between “the sufficiency of credible evidence” and “the credibility of sufficient evidence,” an Illinois appellate court recently held that a fingerprint examiner’s expert testimony, no matter how credible it might have been, was insufficient to support a burglary defendant’s conviction. The opinion underscores the need for criminal defense lawyers to counter every prosecution expert with the testimony of a defense expert when there is any possibility that the prosecution expert’s testimony is based on bad science.

Facts of the Case

Tom Slowinski returned home to find that his home had been burglarized. Among other missing items, Slowinski noticed that headphones had been removed from a case. An evidence technician lifted four latent fingerprints from the case.

For reasons that the appellate opinion does not explain, a police detective questioned John Cline about the burglary. Cline denied having been inside the Slowinski home or in his neighborhood. Cline and Slowinski both stated that they did not know each other.

Daniel Dennewitz, a police officer who had been trained in the area of fingerprint examination and identification, examined the fingerprints taken from the headphone case and compared them to Cline’s fingerprints.

Dennewitz determined that three of the four lifted fingerprints lacked sufficient detail to make a comparison. Dennewitz identified the fourth as having come from Cline’s finger. On the strength of Dennewitz’s opinion, Cline was arrested and charged with burglary.

The Science of Fingerprint Comparison

Dennewitz testified about his training and experience in examining and identifying fingerprints. His credentials were not seriously challenged. The court determined that he was qualified to testify as an expert.

Dennewitz explained the stages that he followed in comparing the fingerprints. The first stage compares the ridge pads, the flow of the ridges, and the pattern. If the first stage does not exclude the latent print as being consistent with the known print, the analyst compares unique details in the ridge pads that are the same in both the known print and the latent print.

The final stage determines whether the unique details are in the same position. If they coincide, the examiner proclaims them to be from the same source.

Dennewitz identified nine points of comparison on the latent print. He compared them to a print of Cline’s right middle finger and decided they came from the same source.

On cross-examination, Dennewitz admitted that the latent print showed only one side of the finger. He assumed that since the parts he could see were the same on both the latent and known print, the parts he could not see would also be the same.

Inadequate Methodology

The appellate court concluded that Dennewitz did not follow the “standard analytical procedure” for comparing fingerprints. Components of the standard “ACE-V” examination include Analysis, Comparison, Evaluation, and Verification.

During the analysis stage, the examiner determines whether there is sufficient ridge detail to compare the latent fingerprint and the known fingerprint. The comparison stage requires the examiner to perform a visual or measured comparison of unique details in the known and latent prints.

The examiner makes an evaluation by deciding whether there are a sufficient number of unique details of sufficient quality to support an opinion that the two prints came from the same source. Finally, the verification stage requires another examiner to repeat the process and come to the same conclusion.

The court decided that the ACE-V examination method is the “gold standard” that should be followed by fingerprint examiners. Without using the language of the Daubert decision, the court essentially concluded that the ACE-V method is the only reliable methodology for comparing fingerprints.

The court faulted Dennewitz for skipping the verification stage. That stage is critical because courts and analysts have declined to agree upon an objective standard for determining whether “sufficient” unique details justify the conclusion that two prints came from the same source. Since examiners may have conflicting opinions, the verification step helps avoid the bias of witnesses (in this case, a law enforcement officer) who might be tempted to arrive at a conclusion that favors the government.

On appeal, the prosecution argued that Dennewitz could not have testified about any verification that might have been done because that testimony would have been hearsay. The prosecution’s understanding of the hearsay rule as it pertains to an expert who relies on the opinion of a second expert is doubtful, but the appellate court noted that the problem could have easily been resolved by having the second examiner testify.

Improper Assumptions

The court also faulted Dennewitz for making assumptions about the portions of the latent fingerprint he could not see. Dennewitz admitted that the partial fingerprint did not show all of the characteristics of Cline’s fingerprint because the partial fingerprint was incomplete. Dennewitz testified that he based his comparison on the assumption that the missing portion of the fingerprint would have matched the full fingerprint.

The appellate court cited the rule that key elements of a prosecution may not rest on assumptions. If Dennewitz had not testified that he made an assumption, but had said he based his analysis on the information before him, his testimony might not have been so easily challenged.

Using the language of Daubert, however, the question is whether a partial print supplied Dennewitz with adequate data upon which to base a comparison. Dennewitz testified that he found nine unique characteristics in the same location in each print. In 1924, New Scotland Yard decided that 16 points of comparison should be required for a valid determination that two prints came from the same source.

Apparently believing that an objective standard for comparing fingerprints got in the way of giving testimony that is favorable to prosecutors, FBI fingerprint examiners abandoned the notion that a fixed number of points of comparison must exist before deciding that two prints are from the same source. By 1968, the FBI had rejected an objective standard in favor of the examiner’s subjective impression that “enough” points of comparison exist. Subjectivity is, of course, the enemy of science.

When objective standards are feasible, subjective standards undermine the scientific value of expert opinions. One examiner’s subjective belief that “sufficient” points of comparison exist may be contradicted by the subjective opinion of an equally qualified examiner.

In any event, reliable opinions must be based on adequate data. A partial print that permits only nine points of comparison is arguably inadequate to support a conviction, particularly when the partial print is the only evidence of guilt that the prosecution can muster. A police officer’s subjective opinion that “nine is enough” is a questionable basis for convicting a suspect of a crime.

Lesson Learned

While defense counsel cross-examined Dennewitz about the inadequacies of his examination, juries tend to believe that police officers know what they are doing. The Cline case should remind defense attorneys of the value of hiring their own experts.

In a case like Cline’s, it isn’t necessary to have an expert testify that the latent print and Cline’s print were not made by Cline’s finger. An independent expert may or may not have been able to draw that conclusion.

An independent expert could instead have testified that Dennewitz based his opinion on a single partial print that lacked sufficient points of comparison to permit a reliable conclusion to be drawn. That testimony may have been sufficient to inject reasonable doubt and to avoid the need for an appeal.


About T.C. Kelly

Prior to his retirement, T.C. Kelly handled litigation and appeals in state and federal courts across the Midwest. He focused his practice on criminal defense, personal injury, and employment law. He now writes about legal issues for a variety of publications.

About T.C. Kelly

Prior to his retirement, T.C. Kelly handled litigation and appeals in state and federal courts across the Midwest. He focused his practice on criminal defense, personal injury, and employment law. He now writes about legal issues for a variety of publications.