DALLAS (AP) — A U.S. Postal Service worker was found fatally shot inside a mail truck along a busy highway in Dallas on Monday, and investigators are treating the case as a homicide, according to police.

Officers found the worker's body inside the government vehicle around 2:30 a.m. after responding to a reported shooting along Interstate 30 just west of downtown, according to a statement released by Dallas police.

Sr. Cpl. DeMarquis Black said no arrests have been made, and investigators are still trying to determine a possible motive behind the shooting. The victim's name hasn't been released.

The U.S. Postal Service operates two large mail sorting and processing complexes nearby, according to Amanda McMurrey, an inspector with the U.S. Postal Inspection Service , the law enforcement and security arm of the USPS.

Requests sent to the USPS for details about the employee were referred to the inspection service. McMurrey had no immediate information on the employee's route, but she said it isn't unusual for a postal service worker to be on the job before dawn.

"It is routine for postal employees to be making deliveries to stations and other post offices at that time," McMurrey said.

The Dallas Main Post Office, which includes a processing and distribution plant, is on the north side of I-30, she said. A USPS National Distribution Center is located on the south side of the highway, a main route connecting Dallas and Fort Worth.

Any charges in the slaying would be referred to federal prosecutors because the victim worked for a U.S. government agency, according to McMurrey.

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