DALLAS (AP) — A federal grand jury has indicted a Dallas-area man in the killing of a postal worker who was driving an 11-ton (10-metric ton) delivery rig on a Dallas expressway.

A statement by the U.S. Attorney's Office in Dallas said 25-year-old Donnie Arlondo Ferrell of Hutchins is charged with murder of a U.S. officer or employee and a firearms violation. The indictment also charges 24-year-old Bei-jing Tashawna Walker of Hutchins with aiding and abetting Ferrell after the Feb. 19 shooting by helping him avoid arrest.

Both will remain jailed pending trial.

Investigators say 58-year-old Tony 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.