BUFFALO, Iowa (AP) — A federal investigation has concluded a worker wasn't following safety protocols when he was killed last year in a limestone mine collapse in Scott County.

The Quad-City Times reports a Mine Safety and Health Administration investigation concluded that 52-year-old Ronald Trich Jr. had entered an area of the Linwood Mine that was barricaded due to unsafe conditions when he was killed on Jan. 25, 2017.

Investigators concluded Trich, of Rock Island, Illinois, had entered the area in search of crystals despite being warned twice by management to stop such efforts. Other miners also warned him not to seek crystals in dangerous areas of the mine.

Trich worked as a truck driver at the mine, located near Buffalo. The operation employs 61 people.

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Information from: Quad-City Times, http://www.qctimes.com