Police said Saturday that 52-year-old Yefim Tsirinsky was arrested on charges of murder and strangulation.
Neighbor Donald Solomon said he was in "shock." He said he "couldn't believe" her son had been involved in her death "because he used to take good care of her."
Solomon said Tsirinsky would push around her wheelchair.
Police say Frida Tsirinsky was found unconscious by officers responding to a call at West 12th Street in Coney Island on Friday. The 86-year-old woman was taken to Coney Island Hospital.
She was pronounced dead Saturday.
Police declined to discuss the motive in the killing.
They say the son appeared to be unemployed.