Three people were shot and killed in their Upper West Side Manhattan apartment Thursday, a fourth man was found dead in the backyard, New York Times reported.

The three men shot and killed in their apartment at Amsterdam Avenue and West 84th Street were identified as a man in his 20's, his father and his grandfather.

The fourth man found dead in the backyard is believed to either have plunged or accidently fallen to his death while trying to escape.

According to reports, police believe the fourth man found in the backyard may have been the gunman.

The killings were reported before 2pm EST in the upscale area not known for high crime rates.

The motive behind the killings is unknown.