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
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person
Lead #1What were Mark's activities and social connections in Boulder in March 1978?
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witness
Lead #2Were there any witnesses to Mark's whereabouts on the day he disappeared?
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clue
Lead #3What circumstances led to his disappearance—voluntary departure or foul play?
Mark Bonner, a 23-year-old male, disappeared in Boulder, Colorado on March 20, 1978, and has never been found. The circumstances surrounding his vanishing remain unclear, with limited details about his last known activities or whereabouts. Despite decades passing, this case remains open and investigators continue to seek information that could help solve what happened to him.
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More leads to consider
Beyond the top three above — each detail below could be the thread that pulls this case open.
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evidence
Lead #4Are there any personal effects, vehicle, or other physical evidence related to his case?
Have information about any of these leads?
Even the smallest detail could be the key to solving this case.
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 Seen
Mark Bonner was last seen in Boulder, Colorado 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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Any information, no matter how small, could be crucial to solving this case.
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