Two armed guards had traveled hundreds of miles in a tractor-trailer laden with silver and gold when they started to smell gas.
The odor was so strong they thought they would be sick. So they pulled over to the shoulder of Interstate 95 in Wilson, N.C., to check on their truck, authorities said.
When they got out, they were approached by three men with guns who yelled, "Policia!"
The gunmen tied the guards' hands behind their backs and forced them into a nearby wooded area, authorities said, then placed orange cones on the highway and cut the lock on the trailer. They made off with more than $4 million worth of gold bars, authorities said.
The robbery took about 30 minutes, said Wanda Samuel, chief of staff for the Wilson County Sheriff's Office, which is investigating the Sunday night incident.
"We are looking into all allegations that have been provided to us by the victims, the driver of the truck, the passenger and the witnesses," Samuel said.
The thieves left in a white van, police said, and the two guards stumbled out of the woods and toward the roadway looking for help. Several passersby called 911. Both guards were unharmed, except for some minor scratches.
The truck had been en route to Bridgewater, Mass., from Miami to drop off its valuable load, said Samuel, who refused to identify the company that was to receive the gold and silver. Wilson is about 50 miles east of Raleigh, North Carolina's capital.
The guards are employed by TransValue Inc., a Miami-based company that specializes in transporting valuables. The company has offered a $50,000 reward, Samuel said.