Ernesto Gonzalez Jr., 36, told a Boston Globe reporter Wednesday that he stabbed and dismembered his son while the child was visiting him in August, the newspaper reported.
In a jail house interview, Gonzalez said he lost his temper after his son was "behaving badly." He said the next thing he knew he was stabbing the boy.
Gonzales also reportedly told the newspaper he dismembered his son's body in the bathtub and dumped his remains in trash bins in Lynn, Mass.
"It happened. I was upset. It happened in a moment," he was quoted as saying.
Steve O'Connell, a spokesman for Essex District Attorney Jonathan Blodgett, said the DA's office is investigating the claims.
"We will review the alleged statement of the defendant and determine whether it is truthful or not," he said. "The investigation remains ongoing."