In this week’s episode of Zone 7, Sheryl McCollum talks with forensic DNA expert Suzanna Ryan about how powerful DNA evidence can be and why it is so often misunderstood. They discuss how DNA is analyzed, how touch DNA and mixtures can complicate a case, and how newer tools like genetic genealogy and next-generation sequencing are changing the field. Using the Nancy Guthrie case as an example, Suzanna and Sheryl also explain how private forensic labs can support complex investigations, where their role differs from the FBI, and how CODIS limitations can shape the process.

Highlights:

(0:00) Sheryl McCollum welcomes Suzanna Ryan to Zone 7

(2:30) The four basic steps of DNA analysis and how evidence is processed in the lab

(3:45) The Nancy Guthrie case, private lab testing, and why sending evidence outside the FBI is not a red flag

(7:45) What cell-free DNA is, why the term “touch DNA” can be misleading, and how secondary transfer works

(9:45) DNA mixtures and how multiple contributors can be found on a single piece of evidence

(14:00) Why clothing evidence should always be collected and packaged separately

(15:45) How long seminal fluid can remain detectable and when Y-STR testing becomes useful

(21:00) Why private labs cannot directly access CODIS, how that creates bottlenecks, and legislative changes in the works

(27:30) Genetic genealogy, CODIS, and familial searching

(30:15) The future of DNA analysis, including next-generation sequencing and emerging forensic tools

Guest Bio:

Suzanna Ryan is a forensic serologist and DNA analyst with more than two decades of experience in DNA casework, technical review, and forensic consulting. She is the laboratory director of Pure Gold Forensics and has worked in both private and public forensic laboratories throughout her career. Suzanna has been qualified and testified as an expert in forensic serology and DNA analysis more than 140 times.

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Sheryl “Mac” McCollum is an active crime scene investigator for a Metro Atlanta Police Department and the director of the Cold Case Investigative Research Institute, which partners with colleges and universities nationwide. With more than 4 decades of experience, she has worked on thousands of cold cases using her investigative system, The Last 24/361, which integrates evidence, media, and advanced forensic testing.

Her work on high-profile cases, including The Boston Strangler, Natalie Holloway, Tupac Shakur and the Moore’s Ford Bridge lynching, led to her Emmy Award for CSI: Atlanta and induction into the National Law Enforcement Hall of Fame in 2023.

Social Links:

Email: coldcase2004@gmail.com

Twitter: @ColdCaseTips

Facebook: @sheryl.mccollum

Instagram: @officialzone7podcast

Preorder Sheryl’s upcoming book, Swans Don’t Swim in a Sewer: Lessons in Life, Justice, and Joy from a Forensic Scientist, releasing May 12, 2026.

https://www.simonandschuster.com/books/Swans-Dont-Swim-in-a-Sewer/Sheryl-Mac-McCollum/9798895652824

 

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