KIMBALL --  A fatal explosion at a central Minnesota post office remains a mystery 40 years later.

A bomb rocked the Kimball Post Office early on the morning of May 13, 1976. Assistant Postmaster Ivend Holen was alone in the building and was killed in the blast.

The bomb was delivered to Kimball from a bulk mail station in Minneapolis the morning of the explosion.

An investigation revealed the bomb was most likely meant to reach someone on the north side of Kimball, and that it was assembled and mailed by someone from the Kimball area. No motive has been determined.

A spokesman for the United States Postal Inspection Service says there are no new leads that can be released. But a $100,000 reward is being offered.

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