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DES MOINES, IOWA (AP) -- A reward in the case of a gunman targeting liquid propane tanks at hog operations in Iowa has grown to $10,000.

Authorities say eight tanks have been ruptured on hog farms in Calhoun and Sac counties.

Officials believe someone with a high-powered rifle is shooting the tanks.

There have been two rounds of shootings - one on July 21 and another on Sept. 23.

No one has been injured.

Calhoun County Sheriff Bill Davis says a bullet ricocheted and went through an office building.

He also says if there's an ignition source, a tank could explode.

Only tanks at hog operations have been targeted.

Information from: The Des Moines Register, http://www.desmoinesregister.com

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