Officers discovered the bodies of the 20-year-old shooter and his victims at about 11:40 a.m. after receiving a report of a family dispute at the two-story house on 225th Street in the Cambria Heights neighborhood.
The bodies of the three victims — the mother, 44, her live-in boyfriend, 47, who was in a wheelchair, and another woman, who was a home health care worker — were found on the ground floor of the home, police said. The shooter's body was discovered with a gun on the second floor.
Police did not immediately release the names of the victims, but a distraught woman who spoke to reporters at the scene identified the 44-year-old as her sister, Sonia Taylor. She claimed that the family had recently tried to get authorities to intervene after the shooter threatened to kill his mother.
The woman, Ann Taylor, said her sister "exhausted every method and nobody did anything."
The names of the victims were not immediately released.
The well-maintained neighborhood is within a few blocks of Belmont Park racetrack, and lined with trees and manicured lawns.
The street, between 115th Street and Linden Boulevard on the Queens-Nassau County line, was cordoned off as police and a team from the medical examiner's office arrived on the scene.