Story highlights 15 stores may have been affected, county health department says

The suspect sprayed a mixture of water, hand cleaner and mice poison, FBI says

(CNN) A man who went into multiple Michigan grocery stores and sprayed a poisonous mixture on open food is in custody, according to the FBI.

About 15 stores -- including a Whole Foods Market and a Kroger -- in Ann Arbor, Flint, Midland, Birch Run and Saline may have been targeted, according to the Washtenaw County Public Health Department.

"It's just absolutely crazy. Why would somebody do that?" a customer outside Whole Foods Market told CNN affiliate WDIV.

Though the department says it has not received any "unusual reports of illness," it says it's received reports of vomiting and diarrhea that "are being actively investigated for possible connection to this incident."

The suspect admitted to spraying a "potentially hazardous material" -- a liquid combination of water, hand cleaner and mice poison -- on produce in three stores within the past two weeks, the FBI said.

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