Anatomy of Murder: "The Man Beneath the Floorboards (Mark Koster)"

Podcast: Anatomy of Murder (Audiochuck)
Hosts: Anna-Sigga Nicolazzi & Scott Weinberger
Episode Date: January 20, 2026

Episode Overview

This gripping episode dissects the decades-old murder of Mark Koster, whose mummified body was discovered hidden under debris and kitty litter in the basement of his own Iowa home years after his disappearance. Hosts Anna-Sigga Nicolazzi and Scott Weinberger methodically walk listeners through the painstaking investigation, the challenges posed by a dilapidated crime scene, the use of digital forensics, and the nuanced pursuit of justice for the victim and his family.

Key Discussion Points & Insights

1. Discovery of the Body

• A shocking find:
  • A new homeowner, while renovating a rundown property in Sac City, Iowa, discovers a body under a water heater in the basement ([02:04–03:33]).
  • The basement was described as “a labyrinth of retaining walls” (A, [03:46]) and “a secondary trash receptacle” (C, [04:07]), making detection difficult during previous police searches.
• State of the body:
  • The body was found mummified, covered in about 10 pounds of kitty litter, which preserved it and masked odors (A, [05:51]).
  • “It’s exactly the type of thing that when you’re watching certain movies … you can almost picture the skin stretched … that’s what investigators saw” (D, [05:03]).

2. Identification and Backstory

• Identifying Mark Koster:
  • Dental records confirmed the body as Mark Koster, a recluse who had grown estranged from his large family ([07:31–08:20]).
• Family & lifestyle:
  • “He got up in the morning, tinkered with an old computer and played poker online … he just kind of isolated himself” (A, [08:10, 08:20]).

3. The Missing Persons Case

• Initial police searches fail:
  • Despite two full searches of the home after Koster’s 2009 disappearance, police fail to locate his body due to the basement’s overwhelming clutter ([09:33–10:24]).
  • “I would have never found it unless you told me where it was” (A, [10:24]).
• Legal death declaration:
  • After two years without word, Mark is declared legally dead by a special jury ([11:00–11:24]).

4. Early Investigative Leads

• Clues left behind:
  • A suspicious note: “Gone to Florida with Tom for the winter. See you in the spring.” The phone number leads to a Florida hotel, but no Mark or Tom ever stayed there ([13:04–13:20]).
• Neighbor report:
  • A neighbor recalls a very tall man named “Tom,” often carrying a Pomeranian “like a clutch purse,” living with Mark prior to his disappearance ([14:27–15:14]).

5. Identifying the Suspect

• Tracing ‘Tom’:
  • Investigators first pursue Tom Falke, but he is cleared, leading them to another friend, John Green ([16:12–16:52]).
  • John Green had a history of gambling addiction, tumultuous relationships, and transience ([18:13–18:26]).

6. The Power of Digital Forensics

• Phone records search:
  • County Attorney Ben Smith tenaciously tracks down outdated phone records, despite phone companies’ policies ([18:57–23:08]).
  • “I went through every single phone number, and there was hundreds and hundreds of pages of records” (A, [23:03]).
• Breakthrough:
  • Smith notices suspicious calls to a Mississippi police department, connecting John Green to the time-frame and region ([23:08–24:00]).
• Geographic challenge:
  • John Green is eventually located in rural Georgia living out of a camper with his Pomeranian ([26:49–27:37]).
• High-tech pursuit:
  • Investigators secure a search warrant to track Green’s phone GPS, monitoring his movements remotely ([27:56–28:32]).

7. The Interview & Confession

• The confrontation:
  • Interview takes place in a child-friendly room in Jacksonville, Florida. The casual setting lowers Green’s guard ([29:15–29:43]).
• Breakthrough moment ([35:12–35:29]):
  • Investigators ask, "Did this happen at night or during the day?" Green, head down, answers "at night" – a tacit confession.
  • “Midnight,” Green admits, marking the case’s pivotal confession ([35:29]).
• Details of the crime:
  • Green claims self-defense:
    • “He came after me with a bat … I just simply defended myself” (E, [36:05]).
    • Admits to choking Mark with a bat ([36:44]).
  • Discussion of concealment:
    • Green explains the use of kitty litter was to avoid odor, but his overall actions indicate intentional cover-up, contradicting self-defense claims ([38:34]).

8. Motive

• Explained cause:
  • Green says argument stemmed from “he was mad at me earlier about dinner. I didn't cook the chicken right” (E, [38:58]).
  • Hosts note that many homicides have “small” triggers, but Mark’s life and isolation made him vulnerable ([39:27]).

9. Court Proceedings and Justice

• Trials and mistrial:
  • First trial results in mistrial after a prejudicial comment by an officer ([40:07–41:10]).
• Plea offer declined:
  • Green rejects a 10-year manslaughter deal, insisting on trial ([42:05–42:41]).
• Second trial outcome:
  • Green takes the stand; the jury finds him guilty of second-degree murder – 50-year sentence, eligible for parole after 35 years ([43:04–43:57]).
• Post-trial adjustments:
  • Ben Smith later agrees to reduce the sentence, feeling that lifelong imprisonment for a fight between two friends was not justice ([44:28–45:22]).
  • New deal: 15 years before eligible for release ([45:22]).

Notable Quotes & Memorable Moments

• On the basement discovery:
  “It was almost as if somebody, decades ago, had plans to finish the basement and they just never did.” (A, [04:18])
• On digital forensics:
  “You always get, you know, catch more flies with honey than vinegar. And I always subscribe to that theory.” (A, [22:23])
• On Mark Koster’s isolation:
  “He just kind of isolated himself.” (A, [08:20])
• On the confession:
  “Did this happen at night or during the day?” — “At night.” (A/E, [35:16–35:29])
• On Ben Smith’s sense of justice:
  “It just, to me it wasn't justice. It just did not sit well with me … Him sitting in prison for a fight that started with his friend for the rest of his life was not justice.” (A, [44:28])
• On covering the less publicized murders:
  “Most [cases] never make headlines or get into the newspapers at all. But yet for the victims of those crimes, their families grieve just the same.” (D, [45:53])

Timestamps for Key Segments

• Discovery of the body: [02:16–05:51]
• Police failed searches / Declared dead: [09:02–11:24]
• Neighbor’s "Tom" and the Pomeranian tip: [14:27–15:14]
• Ben Smith’s investigation & phone record breakthrough: [18:57–23:08]
• Locating John Green in Georgia: [26:49–27:37]
• John Green’s confession – pivotal moment: [35:12–35:29]
• Green recounts fight & concealment: [36:05–38:34]
• Trial, mistrial, and plea decision: [40:07–42:41]
• Sentencing and quest for justice: [44:28–45:55]

Tone & Style

The episode maintains a methodical, compassionate, yet unflinching tone—characteristic of true-crime podcasts that strive for empathy with both victim and perpetrator. The hosts frequently reflect on the broader system, the humanity behind the badge, and the search for true justice.

For Listeners: Why This Case Matters

Though Mark Koster’s murder may not have made national headlines, the episode serves as a reminder that every victim’s story is important. The case demonstrates diligent investigative work and the challenges small communities face when tragedy strikes close to home. The handling of the case by Ben Smith also sparks thoughtful discussion about the nature of justice and the value of every human life.

(Episode skips non-content, ads, intros, outros, and focuses on the core story and its investigation.)