Double Loop Podcast



Support the Double Loop Podcast at Double Loop Podcast is a weekly show that features Glenn Langenburg and Eric Ray discussing latent print topics. Current events, the latest trends, intriguing research, and interesting guests. Check back every week for the latest latent print talk.


  • Episode 238 - Dror and Scurich Article

    06/07/2021 Duration: 01h16min

    Glenn Langenburg and Eric Ray review the 2020 article from Itiel Dror and Nicholas Scurich. "(Mis)use of scientific measurements in forensic science" was published in Forensic Science International: Synergy. The article criticizes published accuracy studies in the latent print and firearms disciplines and suggests an alternative method for handling inconclusive decisions and calculating an error rate for the field. The episode details factual errors in almost every part of the article and suggests the real motivation behind these arguments. But first Eric and Glenn read some emails and catch up on our return to conferences.

  • Episode 237 - Testifying After an Error

    25/04/2021 Duration: 01h13min

    Glenn Langenburg and Eric Ray discuss how to testify in court after an error occurs. Examiners nervous about upcoming testimony can find tips whether you made the error or a co-worker made an error and whether it was an erroneous identification or an erroneous exclusion. The court and juries do not expect us to be perfect, and we should claim to be. It's important to be able to discuss the Quality Assurance protocols that our labs have in place. Watch Eric and Glenn compare fingerprints here - And join us for Wed Happy Hour here -

  • Episode 236 - Mindset Paper (Eldridge & Champod, Part Deux!)

    27/03/2021 Duration: 01h06min

    In this episode, the guys return for Round 2 with Dr. Heidi Eldridge and Prof. Christophe Champod. This time, they discuss the second paper arising from the palm print black box study (discussed in DLP Episode #234). The focus in this episode is “Mind-set – How bias leads to errors in friction ridge comparisons” by Eldridge, de Donno, and Champod in Forensic Science Int’l 318 (2021). This paper explores how instances of false positives and false negatives may have resulted from cognitive biases and assumptions formed about the latent print during the examination. The authors discuss some of the differences between mindset in false positives versus false negatives. They end the interview with suggestions for breaking mindset and reducing errors. Link to paper:

  • Episode 235 - Todd Weller Interview

    12/03/2021 Duration: 01h37min

    Glenn Langenburg and Eric Ray are joined by Todd Weller to discuss the firearms/toolmarks discipline. Todd was involved in the NY firearms case from Episode 227 and shares his experiences there. The guys then talk through accuracy studies for firearms examiners and similarities and differences between firearms and fingerprints. Lots to cover in an extra-long episode.

  • Episode 234 - Palm Print Black Box Study

    27/02/2021 Duration: 01h28min

    In this episode, Eric and Glenn are joined by Dr. Heidi Eldridge and Prof, Christophe Champod, the authors of "Testing the accuracy and reliability of palmar friction ridge comparisons - A black box study". The guests describe the design, the aims, and the results of the study. We get into discussions about the meaning and usefulness of error rate statistics and confidence intervals from performance studies such as this. Link to the Article (open source): Link to study results in shinyapp: Link to confidence interval tools in shinyapp: Link to error rate primer prepared by Champod, Eldridge, Lambert:

  • Episode 233 - GYRO Accuracy Paper

    16/02/2021 Duration: 01h09min

    Glenn Langenburg and Eric Ray finally get back on track with a review of a recent article on GYRO markings. "Evaluating the Accuracy and Weight of Confidence in Examiner Minutiae Annotations" was written by Jeremy John and Henry Swofford and published in the JFI. The study measured whether examiners placed minutiae markers on true minutiae using Green, Yellow, and Red markers. It then compared the color choices of examiners against the color choices of the automatic LQMetric and DFIQI algorithms. Eric and Glenn will soon be publishing videos of themselves conducting comparisons, using GYRO, and discussing their similarities and differences. Keep an eye out for those coming soon. Also, the 8pm (ET) Wednesday night virtual Happy Hour continues at

  • Episode 232 - Differing Conclusions Article

    06/01/2021 Duration: 01h29min

    Glenn Langenburg and Eric Ray review the newest article from Austin Hicklin, Bradford Ulery, Madeline Ausdemore, and JoAnn Buscaglia. Why do latent fingerprint examiners differ in their conclusions? reviews data from the Black Box, White Box, and Eye Tracking papers, summarizes trends through all of that research, and recommends changes for the fingerprint field.

  • Episode 231 - Review of Carter, et al. (2020) Paper on Conclusion Scales

    24/11/2020 Duration: 01h10min

    After some Halloween talk, Eric and Glenn discuss this episode’s research article: “The Utility of Expanded Conclusion Scales During Latent Print Examinations” by Carter, Vogelsand, Vanderkolk, and Busey in J Forensic Sciences (online, 2020). This study examines the results of 27 experts who completed 30 comparisons under a 3-point SWGAST scale versus 30 comparisons under a 5-point OSAC scale. The guys discuss error rates, changes in apparent decision thresholds, and the rate of misleading evidence of “support for…” decisions. Article: Interpol Paper Reference:

  • Episode 230 - Fingerprint Error Rate in Close Non-Matches

    28/10/2020 Duration: 01h25min

    In this Halloween episode, Eric and Glenn discuss a new paper published by Koehler and Liu titled “Fingerprint error rate on close non-matches” (Journal of Forensic Sciences, Sept. 2020). The paper raises a lot of discussion between the guys regarding close non-matches, inconclusives, training, and testimony. They each have a different take on some of the key issues in the paper, but in the end identify what common ground on which they agree.

  • Episode 229 - Bob Garrett

    13/10/2020 Duration: 01h22min

    Glenn Langenburg and Eric Ray pay special tribute this week to a giant in the fingerprint world, Bob Garrett. With the passing of Bob and a few other close friends and colleagues, Glenn and Eric want to look back at the contributions of Bob Garrett in particular. In his single year as president of the IAI, he was instrumental in responding to the NAS Report, addressing the McKie controversy, and moving forward the Standardization II Committee. Please join us in remembering Bob and all of the other friends and colleagues that we've recently lost.

  • Episode 228 - Knuckle-Crease Daubert Hearing

    16/09/2020 Duration: 01h30min

    In this episode, Glenn and Eric discuss a recent case Glenn was involved in: a knuckle-crease case. The case had a Daubert hearing in addition to trial testimony for jurors. The guys discuss if non-friction ridge skin associations would meet the Daubert factors. If you were preparing for such a hearing, what research and testing would you need to demonstrate expertise of the expert, or demonstrate reliability of the methods and principles? Does expertise in fingerprints using ACE-V translate to the comparison of non-friction ridge skin or any other objects you might encounter in photographs? Stay tuned…their answers may surprise you!

  • Episode 227 - NY Firearms Case

    02/09/2020 Duration: 01h20min

    Glenn Langenburg and Eric Ray review a recent court decision on firearms testimony. NY v Ross was a recent Frye case where the testimony of firearms examiners was restricted to only class characteristics. Was this a fair decision? Did the judge raise good points? How does this case relate to latent print testimony and latent print accuracy studies? Join us for an hour of fun talk as we dive deep into the nerdy intersection of science and law.

  • Episode 226 - Best Latent Print Books

    20/07/2020 Duration: 01h01min

    Glenn Langenburg and Eric Ray were recently asked which latent print books they recommend the most. This episode they talk through the absolute creme de la creme of fingerprint tomes. New books, old books, green books, blue books. Whether you're developing or comparing ridges, we've got a list of what you need to read. Also make sure to join us Wed nights at 8pm EDT for Virtual Happy Hour at

  • Episode 225 - The Most Dangerous Animal of All Documentary

    01/07/2020 Duration: 01h32min

    This week, the guys review and share their reactions to the documentary “The Most Dangerous Animal of All” (produced by Campfire Productions and available now on F/X and Hulu). This is a story about Gary Stewart who believes his father, Earl Van Best, Jr. was the infamous Zodiac Killer in San Francisco in the 1960s/1970s. The series reveals who Gary is and his obsession with the Zodiac. Then it shows all of the extensive evidence that he and his co-author accumulate to prove Earl Van Best was the Zodiac. Glenn and Eric discuss the forensic evidence in this case and share their views and reactions. At approximately 53:00 minutes we give a spoiler alert as the series and this podcast episode take a turn. We highly recommend watching the 4-part documentary first before hearing our views on this case. Discord link (Wed 5-7PM PST) Webinars:

  • Episode 224 - Forensics in the New Normal

    16/06/2020 Duration: 01h13min

    Glenn Langenburg and Eric Ray take a break from normal interviews and research reviews to host a laid-back happy hour discussion on how things have been different in the past few months in forensic crime labs. Carey Hall, Becca Coutant, and Josh Connelly join our discussion that meanders from discussions on web-based training, remote testimony, recent changes to in lab life, and TV recommendations. Our Discord server is at Happy Hour is Wed's at 8pm EDT.

  • Episode 215 - Aging Latent Prints

    02/06/2020 Duration: 55min

    Eric and Glenn wrap up their “activity level series” by discussing two articles (Girod, et al. 2016; and Hinners, et al. 2020) which propose determination of aging of latent fingerprint residue. The techniques use instrumental techniques to identify breakdown products of various fatty components in latent print residue, and use these results to classify whether a latent print is a couple of days old, or older (up to a week or month old depending on the paper). This is a nice finale to the series to explore what the realities and limitations of aging latent prints entails, rather than relying on visual inspection and qualified “consistent with” statements that previous episodes revealed could be misleading or just plain wrong. Glenn also starts the show by relaying a little bit of his experience joining the new NIST/NIJ Human Factors Expert Working Group on DNA mixture interpretation.

  • Episode 223 - Luke Ryan Interview - Mass Drug Scandal Part 3

    24/05/2020 Duration: 01h56min

    In the final and third part of the series on the Massachusetts drug scandals and Netflix documentary, we interview Luke Ryan, the defense attorney featured in the documentary and who represented several of the clients affected by the scandal. Luke described how and why he fought to uncover the truth that was being swept under the rug by the Attorney General’s office. We also discussed a number of other issues that were not shown in the documentary, including deliberate and willful collusion by the drug chemists to mislead the court, the results of a quality audit that occurred, and early signs that drug chemists were engaged in misconduct for years. Luke also shared his views on a number of criminal justice and social issues such as civil forfeitures, the war on drugs, discovery of predicate questions, and field test kits for narcotics. Settle in for a super-sized episode uncovering the unbelievable and fantastic story behind the Netflix documentary and the perfect storm that could allow such behavior to

  • Episode 222 - How to Fix a Drug Scandal Documentary - Part 2

    06/05/2020 Duration: 01h15min

    Eric and Glenn finish out their discussion of the new Netflix documentary “How to Fix a Drug Scandal” (2020). In this episode we switch our focus on the dry-labbing of drug tests by Annie Dookhan, and how long it took for those tests and convictions from those test to finally get tossed. The episode concludes with the story of Luke Ryan and his crusade to finally find the evidence that clearly demonstrated that Sonja Farak had been using drugs for years and not just months. Join Glenn and Eric on Discord for virtual Latent Print Examiner Happy Hour, Wednesdays 8-10PM EST (5-7PM PST) during the Shelter in Place orders (

  • Episode 217 - Forensic Movie Recommendations during COVID-19

    29/04/2020 Duration: 01h19min

    In the wake of COVID-19 and so many of us staying at home, we decided as an April Fools’ Episode to make a list of movies that we enjoy and feature an aspect of forensic science. Eric and Glenn run down our top 10 movies (with two “so bad, they’re good” recommendations) and a few honorable mentions for you to consider while deciding what movies or shows to binge. We also alert listeners at the end to a call for research, regarding a new “verification practices” survey that you can take.

  • Episode 221 - How to Fix a Drug Scandal Documentary - Part 1

    27/04/2020 Duration: 01h05min

    In the first of two episodes, Glenn and Eric discuss Netflix’s “How to Fix a Drug Scandal” (2020), covering the actions and consequences of two Massachusetts drug chemists. In this episode, they mostly focus on the Sonja Farak aspect, who was a drug chemist, addicted to drugs and stealing drugs from her standards cabinet and evidence. The guys discuss the issue of ‘random drug screenings’ of crime lab employees and the lack of other various controls in the U.S. The lack of controls can allow circumstances like this to occur, here and elsewhere, undetected for a long time. They also share some personal experiences from their past related to friends/co-workers with serious drug problems. Also, they remind everyone to join them on Discord for virtual Latent Print Examiner Happy Hour, Wednesdays 8-10PM EST (5-7PM PST) during the Shelter in Place orders (

page 1 from 7