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 228 - Knuckle-Crease Daubert Hearing

    Episode 228 - Knuckle-Crease Daubert Hearing

    16/09/2020 Duração: 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

    Episode 227 - NY Firearms Case

    02/09/2020 Duração: 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

    Episode 226 - Best Latent Print Books

    20/07/2020 Duração: 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

    Episode 225 - The Most Dangerous Animal of All Documentary

    01/07/2020 Duração: 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

    Episode 224 - Forensics in the New Normal

    16/06/2020 Duração: 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

    Episode 215 - Aging Latent Prints

    02/06/2020 Duração: 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

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

    24/05/2020 Duração: 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

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

    06/05/2020 Duração: 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

    Episode 217 - Forensic Movie Recommendations during COVID-19

    29/04/2020 Duração: 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

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

    28/04/2020 Duração: 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 (

  • Episode 220 - Blind QC Research at HFSC

    Episode 220 - Blind QC Research at HFSC

    21/04/2020 Duração: 01h04min

    In this episode, Eric and Glenn start the show discussing a few kind emails and reviews of this podcast. They also talk about a weekly social event online—an online Happy Hour on Discord for Latent Print Examiners and friends of the show. In the main segment, the guys review Hundl et al. (2019) “Implementation of a Blind Quality Control Program in a Forensic Laboratory” in the Journal of Forensic Sciences. This research paper discusses the results of introducing over 140 realistic ground truth cases, without the analysts’ awareness that the case is a test case, at the Houston Forensic Science Center (HFSC) in Houston, Texas, over a period of several years. Join other listeners of the Double Loop Podcast for a LPE Happy Hour on Discord, Wednesdays 5-7pm PDT (8-10pm EDT) at

  • Episode 219 - David Camm Case - Part 2

    Episode 219 - David Camm Case - Part 2

    15/04/2020 Duração: 01h11min

    The case against David Camm is about to be turned on its head. Eric Ray and Glenn Langenburg continue the story with a second and third trial and the introduction of a mountain of evidence against a new suspect. The episode concludes with an in-depth discussion on the importance of considering multiple scenarios in bloodstain pattern and all forensic disciplines. It all ties back to our previous discussions of activity level propositions.

  • Episode 218 - David Camm Case - Part 1

    Episode 218 - David Camm Case - Part 1

    07/04/2020 Duração: 01h03min

    In this multi-part series on the Indiana v. David Camm case, Eric and Glenn review the evidence over multiple episodes. In this first episode they review the evidence of the Prosecution and the first trial. There is discussion regarding latent print evidence, DNA evidence, crime scene reconstruction, medical examiner findings, and blood stain pattern evidence. The blood stain evidence is fairly critical in placing David Camm at the scene of a triple homicide (his wife and two young children).

  • Episode 216 - OSAC Update and Travel Stories

    Episode 216 - OSAC Update and Travel Stories

    19/03/2020 Duração: 01h06min

    Glenn Langenburg returns from international travels (just in time) and brings stories from distant lands of England and Minnesota. As the discussion turns to conclusions, Eric Ray brings an update from the OSAC Friction Ridge Subcommittee. Check the NIST OSAC website in the near future for updated versions of Friction Ridge Subcommittee proposed standards.

  • Episode 214 - Simon Bunter Interview

    Episode 214 - Simon Bunter Interview

    24/02/2020 Duração: 01h11min

    Glenn Langenburg is joined by Simon Bunter from Keith Borer Consultants to discuss a number of cases where activity level propositions were key factors. Can a print survive after the surface is cleaned? What if the surface is painted over? Simon tells some amazing stories that should make every latent print examiner question the timeline of when a latent print was left on a surface.

  • Episode 213 - Anouk de Ronde Interview

    Episode 213 - Anouk de Ronde Interview

    04/02/2020 Duração: 01h05min

    Eric Ray and Glenn Langenburg are joined by Anouk de Ronde from the Amsterdam University of Applied Sciences to continue the discussion on activity level propositions. Anouk has published on how to construct a logical framework for considering all the information in a latent print to assist in establishing probabilities for competing hypotheses. Did he climb the railing or just lean against it? Was the pillowcase changed or was the pillow pressed down? Just like you wouldn't reach an Identification without looking at each individual minutiae, this framework allows for examination of each data point before making a conclusion on the likelihood of different activity level propositions.

  • Episode 212 - Activity Level

    Episode 212 - Activity Level

    15/01/2020 Duração: 01h05min

    In this episode Glenn and Eric dig into ‘activity level propositions’, which will start a series of episodes that takes a deep dive into this topic. We lay the groundwork for the topic by discussing fundamental forensic science papers, such as Evett, et al. “The impact of the principles of evidence interpretation on the structure and content of statements” (Science & Justice, 2000) and other works by Cook and Jackson. We highlight the need for formal declaration of propositions regarding ‘source’, ‘activity’, and ‘crime (offense)’ levels. Lastly, we discuss aging (time since deposition) of latent prints and the dangers of these statements based on a visual exam alone. We reference Girod, Ramotowski, et al. “Fingermark age determinations: Legal considerations, review of the literature, and practical propositions” (For Sci Intl, 2016) for important points here. Also Glenn has some news at the beginning of the show to share with Eric regarding DNA.

  • Episode 211 - OSAC  ASB Update

    Episode 211 - OSAC & ASB Update

    08/01/2020 Duração: 01h17min

    Eric Ray and Glenn Langenburg get passionate about policies. Stirred up about standards. PO'd about SDO's. After a quick refresher on how NIST, OSAC, AAFS, and ASB fit together in the Standards Development process, Eric and Glenn give an update on the draft standards for latent prints. Where are the standards that we've been waiting for? There was a recent meeting the Friction Ridge group with ASB, and things did not go well for those of us that would like to see the process move forward. While you're waiting for things to move forward, don't forget to check out the Double Loop Podcast merch store at

  • Episode 210 - Brendan Max Interview

    Episode 210 - Brendan Max Interview

    16/12/2019 Duração: 01h16min

    In this episode, Glenn and Eric interview Brendan Max, Chief of the Cook County Public Defender Forensic Science Unit in Illinois. They discuss his new article “Assessing Latent Print Proficiency Tests: Lofty Aims, Straightforward Samples, and the Implications of Non-Expert Performance” (Max, Cavise, and Gutierrez in JFI 2019;69(3)). Brendan shares his views on proficiency tests: are they meaningful? What about verifications in proficiency testing? What does it mean to ‘fail’ a test? How do lawyers and judges view proficiency tests? He describes his basic strategy for litigating forensic evidence and explains why the research in the field of latent prints is so critical. Pay attention towards the end: Eric legitimately stumps Glenn with a great question!

  • Episode 209 - Friction Ridge Process Map

    Episode 209 - Friction Ridge Process Map

    09/12/2019 Duração: 01h07min

    Eric Ray and Glenn Langenburg talk through the latest document out of the OSAC Friction Ridge Subcommttee. Last month they released an updated, and detailed, process map for friction ridge examinations. Follow along by downloading the pdf from the OSAC FRS website, Eric and Glenn are also happy to announce the Double Loop Podcast merch store. Go to, click on the Store tab, and help support the show.

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