The King County Medical Examiner's Office in Seattle said Mantenuto died of a gunshot wound to the head Monday. It ruled his death a suicide.
Des Moines police says he was found in his car at Saltwater State Park in the city Monday afternoon.
Army First Special Forces unit commander Col. Guillaume Beaurpere said in a Facebook post that the Army staff sergeant will be remembered "for his passionate love for his family and his commitment to the health of the force." A spokeswoman with Joint Base-Lewis McChord, where Mantenuto and his family lived, confirmed the post.
Beaurpere said Mantenuto is survived by his wife and two children.
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