Ocean County Prosecutor Marlene Lynch Ford said Tuesday that a preliminary investigation found "no indication of foul play or trauma."
The 2-year-old victim, identified by authorities only by the initials J.C., was reported missing by her mother, Marina Matias, shortly before 5 p.m. Monday. She had been playing in the yard with four siblings.
Search teams found a 3-foot-wide hole in the yard that led to a septic tank, and the Public Works Department was called to pump water from the tank. The girl's body was found inside it around 7:30 p.m.
Toys were strewn about the yard of the ramshackle property on Tuesday, and the front door of the small house sat open. Police tape cordoned off the area where the top of the tank had been covered with dirt. The tank sat just a few feet outside the back door to the home, next to an outbuilding.
Public records listed the property's owners as Catherine and Thomas Feeks of Sunnyside, N.Y. A message left at a number listed under their name was not returned.
A man who said he has rented a room in the house from Matias and her husband said he was surprised that the opening to the septic tank was big enough for the girl, whom he called Jenny, to slip through.
The man, who spoke on the condition of anonymity because he said he feared retaliation, said the family is from the Mexican state of Puebla.
He said the father, whom he identified as Erasmo Castro, holds down two factory jobs and that the mother stayed home to take care of their children, including an infant.
Neighbor Richard Castelluci, who has lived next door for nine years, said he thought the family had now abandoned the house. He said it has been rented out to families with children, like other homes in the area.
"It's so sad, you know, you can't bring the kid back," he said.