The truck came to rest in the store's fresh produce section and a photograph posted by the Des Moines Register showed boxes and other debris scattered on the floor.
"At this time, we don't have any reason to believe it was intentional," said Patrol Sgt. Nathan Ludwig, who was at the scene of the crash. Ludwig said officials are investigating all possible scenarios.
The crash just before 10 a.m. killed three people — all outside the vehicle — and injured the driver and another person, Ludwig said. None of those killed or injured were children.
Authorities had not released the identities of those involved by early Thursday afternoon as officials worked to inform family members of the casualties. Ludwig said he did not have the medical conditions of those hurt.
Wal-Mart management said in a statement: "We're heartbroken by what appears to be a tragic accident."
Pella — a city of 10,000 known for its Dutch roots and fully functional 1850s-style windmill — is 38 miles southeast of Des Moines.
Information from: KNIA-AM, http://www.kniakrls.com
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