Police were called by a property manager after a nearby business complained about an odor coming from the residence on Thursday.
Police said the male body was recovered around 1:40 p.m. along the rocks at 158th Street and the Hudson River.
The FBI said Thursday that further tests are still being done, but that lab results show the toxin was used in the mailings.
It is a real house of horrors. Police have confirmed the discovery of human remains inside — from an elderly person who passed away years ago.