On our blog last week, we began exploring the notion that some of the "evidence" in criminal cases is not quite as "scientific" as it seems. Often, juries see certain types of evidence--bite marks, blood spatter, hair analysis, for example--as irrefutable scientific proof that a defendant committed a crime. Instead, we see that this evidence is often based in unproven scientific theory rather than fact. What seems like proof to a jury may just be a lot of filled in blanks and assumptions presented by a self-described forensic expert.
Fingerprint Forensic Evidence
One type of evidence that is often used to help secure a criminal conviction is fingerprint analysis. It would seem, on the surface, as if fingerprint analysis would be a sure-fire method of identification. After all, no two fingerprints are alike, right? Although there are some problems with making that assumption, the greater issue lies in the fact that detectives rarely find a full, intact print at the scene of a crime. Instead, they must rely on partial prints and "expert" analysis.
In analyzing fingerprints, forensic experts examine a partial print to determine how many points, defined by ridges and whorls of the fingerprint, match with the fingerprint of a suspect. But even among experts, there is disagreement about how many points must correlate between the two in order to determine a "match." Some experts say a match can be determined by matching as few as 12 points; others say 20 points is necessary to determine a match. If experts can't agree on what makes a definitive match, how can juries be expected to determine the answer?
Furthermore, even if full, complete fingerprint was lifted from a crime scene, even if the print could be proven beyond all doubt to belong to a suspect, the print itself does not mean the suspect had anything to do with the crime. It only proves that he or she was in that location at some point in time, possibly days or even weeks before the crime occurred.
Certainly, fingerprint analysis can be useful in helping law enforcement to identify a suspect, but it is hardly the irrefutable scientific evidence that proves a defendant committed a crime. In fact, some federal courts have ruled that fingerprint evidence fails to meet the United States Supreme Court's standards of scientific evidence, known as the Daubert trilogy:
If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case.
Most courts, however, allow expert witnesses to testify whether or not a fingerprint discovered as evidence is considered to be a match. It is up to the jurors to determine how reliable they believe that testimony and evidence to be.
As ingrained as fingerprint evidence is as a part of criminal investigation and prosecution, it seems unlikely that courts will completely exclude it as admissible evidence any time soon. In order to change public perception of fingerprint evidence as undeniable proof, it will likely take a glaring and obvious destruction of the theories of fingerprint analysis to change things.
What Does a Criminal Defense Attorney Do With Fingerprint Evidence?
A criminal defense attorney uses fingerprint evidence as both a tool to challenge the prosecution. Defense attorneys also use fingerprint evidence support their arguments. Fingerprints are often presented as scientific and conclusive. They are neither. How they were collected, preserved, analyzed, and interpreted matters as much as whether they exist at all.
One important way criminal defense attorneys use fingerprint forensic evidence is challenging reliability. The defense attorneys at Phillips & Associates examines how fingerprints were lifted, whether contamination occurred, and whether proper chain of custody was maintained. Partial prints are common. Smudged prints are common. Subjective interpretation plays a role in comparison. An attorney may challenge the qualifications of the analyst, the methodology used, or whether confirmation bias influenced the match. Errors happen. Documented errors.
A defense attorney also focuses on context and timing. Fingerprints do not show when a person touched an object. A print may place someone at a location at some point. It does not place them there during a crime. Attorneys use this limitation aggressively. Lawful presence, prior contact, shared access, or innocent handling can explain a print without criminal involvement. That distinction matters to juries.
In some cases, fingerprint evidence is used affirmatively. The absence of a defendant’s fingerprints where they would reasonably be expected can undermine the prosecution’s narrative. Alternatively, unidentified prints may suggest another person’s involvement. Defense attorneys may seek independent analysis or expert testimony to present alternative interpretations.
