The shooting happened in the yard of a home on McCormick Drive in Toms River, Ocean County.
Police say the two children played outside the shooter's house most of the day on Monday. But just after 6:30 p.m. the 4-year-old took a loaded .22 caliber rifle from his parents' home and shot the 6-year-old in the head.
The 4-year-old's mother called 9-1-1 and the victim was airlifted to the hospital.
The victim was flown to Jersey Shore Medical Center where he died Tuesday night from his injuries.
The shooters family did return home on Monday but did not want to talk.
Today, we spoke with the victim's uncle, Daniel Watkins who told Action News, "The bullet went into his head."
Daniel Watkins is asking everyone to keep his family in their thoughts and prayers.
"It's really difficult to deal with, something that should have never happened...It's horrible," said Watkins.
Family friend Danella Magiera says the victim's aunt told her, it started out as innocent child's play. "They were playing, I guess pretend like shooting and the little boy, I guess knew where the gun was and got it, because he didn't know."
Neighbors agree that both children are innocent but they also want to know why the 4 year old had access to a loaded rifle.
Investigators say police left the home with several firearms, they found inside the home.
Neighbor, Debbie Coto said, "I'm angry about the dad that he had these guns, because they took more out last night. The cops were here all night long."
Another neighbor, Elaine Isaacson said, "If a person in a family has a gun, lock the darn thing up."
There have been no charges have been filed, so far, in the case.
Police and prosecutors say they are working to gather evidence to move forward. They need to find out exactly where the gun was in the home.
Ocean County Prosecutor, Joseph Coronato says, "There's been no discussions made one way or another on how we are going to proceed, other than, we are collecting all the facts and once we get all the facts, we'll make a determination."