Christopher Sosa Lopez, 28, whose most recent address is in Englewood, was charged with robbery in connection with the Feb. 10 assault, Capt. Fred Pulice said.
Lopez had driven Ronald A. Benitez Santana, a 31-year-old Dominican national who lives in the Bronx, to the postal annex on Smith Street earlier that day, Pulice said.
Officers responding to a call of two suspicious men casing the facility found Lopez sitting in an unregistered vehicle, the captain said.
He told them that he and Santana, whom he identified as his cousin, had come looking for a specific delivery but that his cousin had left.
Police impounded the vehicle and gave Lopez a summons.
A short time later, the postal carrier found Santana taking cellphone photos of the contents of his truck parked on nearby West Palisade Avenue, Pulice said.
"Can I help you?" the carrier asked him.
Santana said a package intended for him was inside, then showed the carrier a tracking app on his phone that listed it, Pulice said.
The carrier told police he retrieved the package, then explained to the stranger that he only needed to see some ID before he could release it, the captain said.
When Santana said he didn't have any, the carrier told him he was sorry but had to follow the rules.
Santana then grabbed hold of the package and a struggle ensued, Pulice said.
The two fell to the ground, wrestling, he said, before Santana suddenly shouted, "Where's my knife? Where's my knife?"
The carrier said he let go at that point and the mugger ran off with the delivery.
Coming Santana's way on foot was Lopez, who'd walked there from the postal facility.
Santana "threw him the package and they ran in different directions," Pulice said.
Englewood detectives quickly identified Santana and obtained an arrest warrant that turned up during a New Jersey State Police stop earlier this month.
Santana spent six days in the county lockup before being released last Wednesday. He's charged with robbery and conspiracy.
Lopez, meanwhile, remained held in the Bergen County Jail on Wednesday, March 16, pending a court appearance after turning himself in to police on Tuesday.
Authorities never did find out what was in the package.
Click here to follow Daily Voice North Hunterdon and receive free news updates.