A 24-year-old man told investigators he shot and killed his mother and brother, then chopped up their bodies and dumped them into the Harlem River, police said.
Lamar Platt was arrested Sunday on murder charges. No information was immediately available Tuesday morning on whether he had a lawyer.
Police came to the Bronx apartment Platt shared with his mother and 22-year-old brother on Sunday to investigate a report by Platt's grandmother that she had not heard from the family since Nov. 18, police said Monday.
When investigators arrived, they found a trail of blood in the apartment and Platt outside, who admitted to killing his mother, 45-year-old Marlene Platt, and brother, Nashan Platt, police said.
The motive for the killings and exactly when they occurred were unclear.
Police used patrol boats, helicopters and scuba divers to search the river Monday, but did not find any remains.
The search for the bodies will resume Tuesday morning in the river, an 8-mile-long tidal strait that separates Manhattan from the Bronx.