NEW YORK (CBSNewYork) – A 65-year-old man died Wednesday after being punched and falling onto the subway tracks during a dispute in Brooklyn.

As CBS2’s Valerie Castro reported, a large contingent from the NYPD gathered at the Jay Street-MetroTech station in downtown Brooklyn Wednesday afternoon after the push onto the subway tracks turned into a homicide investigation.

The incident happened shortly after 2:30 p.m. Wednesday on the southbound R Train platform at the station, near Jay and Willoughby streets.

An eyewitness told police the suspect was talking to himself before he approached the victim — identified as Jacinto Suarez of Staten Island — who asked him to leave him alone. The suspect started to walk away, but turned around and punched the victim in the face, causing him to fall onto the tracks and hit his head.

“The male asked him to get away,” said NYPD Transit Bureau Assistant Chief Vincent Coogan. “At this point, the person did start to walk away, but turned around and punched the 65-year-old male.”

Suarez went into cardiac arrest and was rushed to The Brooklyn Hospital Center, where he died.

Police said Suarez was not hit by an oncoming train because he was rescued by other commuters.

“It’s believed good Samaritans picked him up and placed him back on to the platform,” Coogan said.

Police said the 18-year-old suspect was quickly taken into custody by a nearby officer.

The investigation caused serious afternoon subway delays.

“You may have to make other arrangements,” a police officer told commuters at the scene. “The train is not coming in for awhile.”

Kim Simmons said a violent incident like this is nothing new to her after 22 years as an MTA supervisor.

“A think there’s a lot of mental illness, and people are just out of their minds. They’re just out of their minds,” Simmons said. “Working for the Transit Authority for so many years, I just watch, I’m just very cautious. I watch all the time.”

Sources said the 18-year-old suspect was being questioned here at the 84th Precinct and was awaiting charges late Wednesday.