The police said that the report had come from the Emergency Medical Service at 9:20 in the morning on December 31.
State Police detained the dead boy's mother's partner on suspicion of committing a criminal offense. The man has previously been seen by the police for criminal offenses of a maneuvering nature.
The child's body has been sent to an expert examination to determine the cause of death.
The police launched criminal proceedings regarding intentional serious bodily injury caused by negligence leading to the death of the victim.
Until now, the family had not been on the police radar.
The version of murder by negligence is being investigated, but it is an initial qualification and, if new facts are revealed, it could be changed, the police said.