Investigators say 27-year-old Derek Tudor told police he suffocated 60-year-old Frank Soucie, whose body was found in a bag buried in the backyard of his Ridgewood home on Monday.
Tudor walked into the police station Wednesday with his biological father, crying, and turned himself in after the remains were discovered.
Tudor reportedly has has prior arrests for forcible touching and turnstile jumping.
Soucie, a retired postal worker and father of two adult sons, was last seen April 22. A neighbor called police after see someone throwing away an unusually large bag.
When officers arrived at the scene, they found a charred sleeping bag in the trash and a freshly-dug grave in the backyard with body parts in it, covered with a sheet.
Ammonia and gloves were also found on the roof.
Soucie was well known in the neighborhood.
"They call him the security guard, because he's always outside," neighbor Ada Zappavigne said. "Twenty-four hours, day and night, 4 o'clock in the morning."
Detectives have also spoken to Soucie's girlfriend, 54-year-old Stephanie Nerni, but she is not expected to be charged in connection with his disappearance and death.