NEW YORK (CBSNewYork) — A $2,000 reward is being offered following two vicious attacks in Riverside Park.

Jessica Rieske said she was surprised when a strange man approached her as she walked her dogs around 11 p.m. Thursday.

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“He was bleeding a lot from his head,” she said. “He had been beaten pretty badly. The whole left side of his face was swollen.”

Police said four men attacked the 21-year-old man at 68th Street by the Hudson River as he was coming home from John Jay College. They threw a bag over his head, beat him with some sort of object and then stole his phone, wallet and laptop.

“I walked him home and we got him an ambulance and then the police came,” Rieske said.

Police believe that same group attacked a homeless man just an hour and a half before as he sat on a park bench at 72nd and Riverside Drive.

Investigators say the men threw him into the river after taking his bag. A woman, who did not want to be identified, found him the next morning.

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“I see a man whose feet are submerged in the river, whose clinging to the wall to stay above water,” she said.

Police are now stepping up patrols in the area, especially at night.

Councilwoman Helen Rosenthal, who represents the area, says the events are alarming.

“We haven’t seen incidents like this for years,” said Rosenthal.

But she says police are posting reward signs across the walkway, hoping someone knows whose responsible.

Both victims were treated at a hospital. The 21-year-old has been released, but there’s no word on the condition of the homeless man.

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