The robbery happened at about 7:20 p.m. Tuesday as the postal worker was making his way back to his truck, WWJ-TV, Detroit, reported.
A man approached the postal worker, showed him a handgun, and forced him to the ground, police said. The suspect then took the worker's keys to his truck, at which point he was joined by another man, police said.
The two men then went through the truck and stole several packages before fleeing on foot, police said.
Police said they were unsure of how many packages were stolen or their contents.
The U.S. Postal Inspection Service has offered a $10,000 reward for information leading to an arrest and conviction in the case.
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