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 was Mark Bonner's routine and social connections in Boulder in March 1978?
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witness
Lead #2Did anyone see Mark on March 20, 1978, or in the days immediately before his disappearance?
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clue
Lead #3Were there any vehicles or individuals of interest reported in Boulder around the time of his disappearance?
Mark Bonner, a 23-year-old white male, disappeared in Boulder, Colorado on March 20, 1978, and has never been found. Standing 6'3" with distinctive strawberry blonde hair and blue eyes, he vanished without explanation during a period when Boulder was experiencing several unsolved disappearances. Nearly five decades later, the circumstances of his disappearance remain unknown, and investigators continue to seek information from anyone who may have encountered him or witnessed relevant events.
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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.
⏰
timeline
Lead #4What specific activities or locations was Mark known to frequent in Boulder?
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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:June 12, 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:June 12, 2026
Have Information?
Any information, no matter how small, could be crucial to solving this case.
Phone: 3034413600
You can remain anonymous