NEW YORK (CBSNewYork) — Mail carriers in the Bronx were on high alert after a rash of muggings that sent four postal workers to the hospital.

The attackers targeted letter carriers at least four times over the last year and twice in the last three months alone in various neighborhoods throughout the Bronx.

Each time, the NYPD said, they shoved the unarmed postal worker to the ground and stole a master mailbox key that gives the thieves access to dozens of mailboxes.

In at least one case, the attackers threatened their victim at gunpoint.

Residents were alarmed at the brazen attacks.

“Oh my goodness, that’s horrible,” said Carrie Davis, High Bridge resident.

Police believe a group of several men was behind all the assaults. They released a sketch of a suspect in the most recent incident, described to investigators as a Black man between 18 and 22-years-old, about 5’6″ and weighing around 175 lbs.

As investigators worked to stop the assaults, they were also trying to figure out the motive.

“I guess with the whole income tax checks coming in, I guess that’s what they’re looking out for,” said Noel Ferreral of Tremont.

“I might have to get a PO Box or something so that I can pick it up myself personally,” said Richard Pacheco of High Bridge.

Postal workers go into every neighborhood in the city, good and bad, with virtually no protection. They said they’re afraid for their safety.

In a statement, the National Association of Letter Carriers told CBS 2 “There seems to be a rash right now. This is nothing new but the frequency of the attacks is alarming, and we are appalled at what’s happening here.”

If and when the suspects are caught, they’ll face federal mail charges.

The mail carriers union was pushing for all postal workers to carry stickers, reminding the public that any attack is a federal offense.

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