DALLAS — Investigators have arrested a man who they say shot and killed a postal worker while he was driving an 11-ton delivery rig on a Dallas highway.

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U.S. Postal Inspector Amanda McMurrey says postal inspectors in cooperation with the Dallas Police Department arrested 25-year-old Donnie Ferrell of Hutchins. McMurrey says federal authorities will determine the exact charges, but Ferrell will appear before a U.S. Magistrate judge Thursday.

Federal investigators had offered a $50,000 reward in the early Monday shooting that left 58-year-old Tony Mosby dead.

Investigators say Mosby was driving the rig, known as a box truck, when he was shot. He was found dead in the truck, which had crashed into a guardrail on Interstate 30 near downtown Dallas.