"The manner of death has not been established," DeFazio said.
"It could be an accident, but at this point, that has not been established," he said.
DeFazio said the boy was likely still alive when he was moved. But who moved him, when, and why remained unclear Saturday night.
"That, of course, is a very critical part of the investigation," DeFazio said.
The boy was shot with a semiautomatic pistol issued to Shaara Green-Sims, a 38-year-old Hudson County corrections officer who was in the Randolph Avenue home at the time along with another child, auhtorities said.
DeFazio said investigators were not yet certain whether anyone else was in the home at the time - or who fired the weapon.
"We have an indication already as to who was there, but the question is was there anybody else," DeFazio said.
He said the boy lived in the area, but it wasn't clear why he was at the house.
Investigators spent several hours at the scene Friday night, but authorities would not say Saturday whether any evidence was taken, citing the open investigation.
Officers closed off a roughly two-block area around Randolph Avenue while investigators were there.