The person at the center of this case
Mark Bonner
Missing Person · Open
48 years waiting · since 1978
Missing Person: Mark Bonner
Justice for Mark Bonner — the trail went cold in 1978, but the truth hasn't.
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Key leads to think about
👁️
witness
Lead #1Who was with Mark Bonner on March 20, 1978, and what were his activities that day?
💡
clue
Lead #2What circumstances led to Mark's disappearance—was it voluntary or involuntary?
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evidence
Lead #3Are there any records, communications, or sightings from the days following March 20, 1978 that could provide leads?
Mark Bonner, a 23-year-old male, disappeared in Boulder, Colorado on March 20, 1978, and has never been found. The circumstances of his disappearance remain unclear, with few details about his last known activities or whereabouts before he vanished. Nearly five decades later, the case remains open and unsolved, and anyone with information about Mark's disappearance is urged to contact the Boulder County Sheriff's Office.
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Official wording
Source Narrative
NamUs case MP25589. Missing person: Mark Bonner.
Last known contact: 1978-03-20 in Boulder, Boulder, CO. Circumstances: Mark Bonner was last seen in Boulder, CO on March 20, 1978.
Demographics: 23 years, Male, White / Caucasian. Physical description: 6 ft 3 in, 150 lbs, hair: Blond/Strawberry, eyes: Blue.
Investigating agency: Boulder County Sheriff's Office | 78-3741.
Timeline of Events
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1978-03-20
Last Known Contact
Mark Bonner was last seen in Boulder, CO on March 20, 1978
Key Locations
Interactive map showing important locations related to this case
Case Information
Incident:March 20, 1978
Last Updated:September 27, 2026
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Phone: 3034413600
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Case Information
Incident:March 20, 1978
Last Updated:September 27, 2026
Have Information?
Any information, no matter how small, could be crucial to solving this case.
Phone: 3034413600
You can remain anonymous