Guide to Latent Print Examination and Friction Ridge Analysis

When TV investigators capture and analyze finger (or other) prints to identify criminals, they are using a forensic technique called “latent print ridge processing.” Crime scene investigators (CSI) and forensic science technicians have used latent print ridge analysis to identify crime suspects for more than a century, and their conclusions are still just as admissible in the courtroom as ever.

The concept of ridge processing is fairly well known, but even the biggest law junkies and CSI fans may not realize just how complicated—albeit promising—the field of forensic print analysis can be. Learn more about the professionals who use it here, as well as the difference between “latent” and “patent” prints; the various applications; lifting techniques; credentialing options; and some of the limitations of these forensic methods.

What Is Latent Print Ridge Analysis?

The concept of print analysis is fairly basic. Experts find finger, palm, or foot prints at a crime scene; analyze them; and, whenever possible, match them with the correct person. The practice, however, is more involved.

Latent vs. Patent Prints

There is more than one way prints are left on a surface, and forensic science technicians classify and analyze them differently. The most common types of prints include latent and patent prints. Patent prints are impressions of prints usually transferred using some type of fluid or chemical, like blood or paint. Latent prints, on the other hand, are formed by the natural oils in one’s skin and transferred by the friction of touch. When TV and movie detectives use special powders or tapes to gather print evidence, they are collecting latent prints.

Ridge Analysis

Print ridges refer to the raised patterns visible on one’s fingertips, palms, toes, and heels. The actual ridges that form the pattern are called loops, arches, and whorls. Ridge analysis is the process in which a print analyst, forensic biologist, or crime scene investigator finds and captures a print to compare its unique pattern with others. Ridge analysis operates on the premise that no two prints are the same, so if a latent fingerprint matches a suspect’s fingerprint, then they were at the scene of the crime, though experts cannot say when. We will address some of the controversy surrounding this concept later. Ridge analysis is considered less reliable than DNA analysis, but it remains a widely-accepted means of gathering forensic evidence.

Applications

Placing potential suspects at the scene of the crime is one of the best known applications of print ridge analysis. Its additional uses include:

• Connecting suspects and victims to the scene of a crime
• Identifying confused, unconscious, deceased, and other unknown people
• Confirming one’s identity for security purposes; this called “biometric security”
• Conducting criminal background checks

How Forensic Scientists Analyze Latent Prints

Print Lifting Techniques

The first thing CSIs or forensic analysts do when they find a fingerprint at a crime scene is “lift” it, meaning they make it visible and capture it in some way. Common print lifting techniques include:

• Dusting or Staining: This is when forensic and CSI professionals “dust” prints by gently applying aluminum flakes or other granular powder to a surface. The powder bonds with the oils that create a print, revealing and defining a print. Professionals might choose to use dye stains instead of powders. They may also apply a sort of glue called cyanoacrylate before dusting or staining to better preserve the print, which is then photographed and transferred to a special card using an adhesive tape. The National Forensic Science Technology Center notes that some fingerprint powders contaminate the evidence, limiting the opportunity for further forensic testing.
• Alternate Light Source (ALS): Alternative Light Source print analysis uses LED lights or special lasers to reveal prints on certain surfaces. Experts can use special dyes and dust (often with cyanoacrylate), camera filters, and photo processing technologies to then capture the print for analysis. The NFSTC reports that ALS is an increasingly popular alternative to dusting or staining as the risk of contamination is much lower.
• Chemical Developers: Latent fingerprints on certain surfaces, like paper or porous materials, can be difficult to lift with dust or dyes. In these cases, professionals use chemical developers that interact with amino acids and other natural residue to reveal latent prints by either coloring them or making them visible under certain lights.

The Latent Print Ridge Analysis Process: ACE-V

Forensic print analysts and CSIs then follow a process known as the “ACE-V method.” Here are the steps that form the acronym:

• Analysis: Print analysts use computers, microscopes, or loupes to identify and count the loops, whorls, and arches that make up its unique pattern and to discern whether it the quality or amount of the pattern is sufficient for further examination. They can also identify scars or other features that could distinguish one person from another.
• Comparison: The next step in latent print ridge analysis compare identified prints to others captured by law enforcement, documented in a crime database, or found elsewhere at the scene. Experts note and compare print features carefully.
• Evaluation: Latent print ridge evaluation is when forensic and CSI experts carefully study two seemingly identical prints and decide the likelihood of the match. Ideally, he or she will identify or exclude a potential suspect, but many results are deemed inconclusive.
• Verification: Once a forensic print analyst concludes his or her evaluation, the print is sent to another independent professional for verification. It is not unusual for a print to undergo several rounds of verification before it is presented as evidence in a criminal trial.

Is Latent Print Ridge Analysis Reliable?

One might think a hundred years of practice and the courtroom admissibility of fingerprint analysis demonstrate the method’s accuracy. Perhaps not. According to the National Institute of Standards and Technology, fingerprint analysis has a questionable scientific basis due, in part, to the subjectivity of examiners’ determinations. A study published in the Proceedings of the National Academy of Sciences agrees, noting that the accuracy of fingerprint analysis has never been ascertained in a large-scale study. In fact, no peer-reviewed study has even verified the well-known belief that individuals’ fingerprints are wholly unique.

Controversy in the Field

There is good cause to doubt the reliability of latent print ridge analysis. In the PNAS study, for instance, researchers challenged 169 latent print analysts to examine 100 prints, then measured the accuracy of their results. In the end, 85 percent of analysts made at least one false negative, leaving an overall false negative rate of 7.5 percent. Real-world cases of latent print misidentification are also not difficult to find. One of the most infamous examples, reports Frontline, was a 2004 bombing in Madrid, Spain, when four independent fingerprint analysts inaccurately concluded that a partial print lifted from a bag of detonators belonged to Oregon lawyer Brandon Mayfield. Examiners later matched the print with an Algerian man, clearing Mayfield of suspicion. Efforts are being made to prevent such mix-ups.

Improving the Accuracy of Print Analysis

The controversy over latent print ridge analysis prompted the American Association for the Advancement of Science to release a report warning print experts never to testify that they can match a print to a single source. Such a determination, noted the report, is “indefensible” and has no scientific foundation. The field had changed. As print examiner Ken Moses—one of the analysts who misidentified Mayfield in Madrid—told Frontline, it became clear that latent print analysis had “taken some sort of a quantum leap because suddenly there were new rules involved.” Efforts are also being made to improve the technologies that allow investigators to match lifted prints with suspects found in criminal databases. According to President’s Council of Advisors on Science and Technology, as reported by American Scientist, automated print identification could reduce bias.

Other Limitations of Latent Print Analysis

As with most other forensic techniques, there are limitations to what even properly-matched prints say about a crime. Latent print ridge analysis cannot determine:

• Sex
• Age
• Race or nationality
• If prints were left before, during, or after a crime
• If prints point to a specific criminal act
• If suspects’ prints remain unchanged by injury or other means

Career Spotlight: Print Analysts and Crime Scene Investigators

Print analysts and crime scene investigators are two sides of the same forensic coin. According to the U.S. Bureau of Labor Statistics, some forensic technicians (e.g., CSI professionals) specialize in collecting evidence at a crime scene while others such as print analysts or forensic biologists stick to conducting analyses in the lab. It is important to distinguish forensic technicians from law enforcement officers and detectives who occasionally find and lift prints, but do not process them.

Education Requirements

According to the BLS, forensic technicians typically need at least a bachelor’s degree in forensic science, chemistry, biology, or a related natural science, though candidates with master’s degrees usually have the best opportunities. Forensic science majors study several forensic methods—toxicology, pathology, blood spatter, and DNA analysis—in addition to print analysis. Technicians who work for police departments may need to complete academy training and become sworn law enforcement officers. Most new professionals work under the direction of experienced techs to receive on-the-job training. Print analysts who work in the laboratory may need to pass a proficiency exam to work independently.

Licensing & Certification

The BLS reports that forensic science technicians, including latent print analysts, are generally not required to become licensed or certified. Professionals who would like to improve their resumes or specialize their training, however, can pursue the following voluntary professional certifications from the International Association for Identification:

• Certified Crime Scene Investigator
• Certified Crime Scene Analyst
• Certified Senior Crime Scene Analyst
• Latent Print Certification
• Tenprint Fingerprint Certification

Career Outlook

The future is bright for forensic technicians. The BLS (Oct. 2017) projects that the demand for forensic technicians will grow by 17 percent between 2016 and 2026—much faster than the average growth expected for all professions nationally. The reasons are varied but include anticipated higher law enforcement caseloads and broader use of forensic techniques as technology improves. Texas, Utah, Virginia, Nevada, and Arkansas should see the fastest growth; California, Florida, Texas, Virginia, and Arizona will add the most jobs overall.

Salary Information

Many factors influence CSIs’ and forensic science technicians’ earnings such as education, experience, and geography. The BLS reports that these professionals earned an average annual salary of $60,690 nationally as of May 2016, though those who worked for the federal government and various consulting services earned considerably more—averages of $101,670 and $74,160, respectively. California, Florida, Texas, Arizona, and New York offered the highest overall salaries that year.

Additional Resources

Readers interested in becoming forensic crime scene investigators or print analysts can learn a great deal about the field by visiting one of the following organizations online:

• American Academy of Forensic Science
• American Board of Criminalistics
• International Crime Scene Investigators Association