An armed good Samaritan thwarted an attempted robbery of a postal worker in a Chicago suburb, according to witnesses. 

“I heard like a bang, bang, and bang, bang, bang, bang, then my mom screams, ‘Tell me those weren’t gunshots,'” a witness who lives in the area told NBC Chicago of the incident in River Grove, Illinois, on Tuesday.

Police said they responded to a neighborhood in the Village of River Grove at about 9:30 a.m. Tuesday, where they discovered a U.S. Postal Service employee was approached by an armed suspect who demanded his keys. 

The mail carrier complied, but an armed witness intervened and fired at the suspect, according to witnesses who spoke to various local media outlets.

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Richard Street in River Grove, Illinois, where a postal worker was reportedly the victim of an attempted robbery. (Google Maps)

Police said “words and gunshots were exchanged,” according to NBC Chicago, and the “the male suspect ran back to the vehicle that dropped him off, and the vehicle fled north on River Road.”

A pair of sisters in the neighborhood said their mom took the postal worker into their home following the gunfire, relaying he was rattled by the incident. 

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“My mom let the mailman inside our house to see if he was OK, because she talks to him regularly. He always comes around here,” the older of the two sisters told NBC Chicago. 

“He was just very distressed, very scared. You could tell he was very nervous from what had just happened,” the other sister said.

 A U.S. Postal Service truck leaves a postal facility on Aug. 15, 2019, in Chicago. (Scott Olson/Getty Images)

The sisters said their neighborhood is generally quiet and they initially believed they heard fireworks, not gunshots. 

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No one was injured during the attempted robbery or gunfire, and the postal vehicle was not stolen.

Local police are working with the United States Postal Inspection Service on the investigation.

Inspectors believe four suspects were involved in the attempted robbery and are considered armed and dangerous. 

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Authorities are offering a $50,000 reward to anyone who offers information that leads to an arrest.