The baby was reported to be in a critical but stable condition at a local hospital Saturday, police said in a statement.
They said earlier his injuries suffered the day before were not believed to be life-threatening.
At about 3am on Friday, the father of the child allegedly broke into the home where the child and mother lived, according to police in Surprise, Arizona, about 30 miles north-west of Phoenix.
The child’s father did not live in the house, police said, adding that the man held the mother and child hostage for several hours before the mother managed to escape.
According to police, the mother contacted a construction crew and requested that they call 911.
While police, including multiple Swat teams, were at the scene, the house caught fire as the child’s father was still inside.
The cause of death is still pending the results of the medical examiner’s full report,” police said in the statement late Saturday. »