A 6-year-old New Jersey boy has died after being shot in the head with a rifle by his 4-year-old neighbor, a law enforcement source says.

Brandon Holt died at Jersey Shore Medical Center, where he was taken with a bullet lodged in his brain Monday evening, police said. He had been playing in the younger boy's yard when he was shot.

"They said he was OK, but you knew he wasn't going to be. And it's not going to be," said neighbor Diane Mlenak. "It's going to change the innocence of all the children around here."

It's not clear if the 4-year-old pulled the trigger or if the rifle accidentally discharged.

Authorities said the two boys were outside the 4-year-old's home in Toms River when the gun, a .22-caliber rifle, went off at about 7 p.m. The parents were nearby and heard the shot; the boy's mother called 911.

The victim's aunt, Danella Magiera, told NBC 4 New York the bullet went through the back of his head and became lodged in his brain.

Toms River Police Chief Michael Mastronardy said the boy was shot from 15 yards away.

Police are investigating how the younger child obtained the rifle from his family's home on McCormick Drive. Authorities said it wasn't known if the rifle was registered to anyone who lives there. It apparently was not the only firearm in the house, according to neighbors, who said they saw investigators remove almost a dozen guns from the home Monday night. Investigators would not detail to NBC 4 New York what was taken.

"I think it's a tragedy that could have been prevented," said another neighbor, Stacey Suppa. "I feel the parents need to be accountable, totally need to be accountable."

Multiple law enforcement sources said the 4-year-old boy and his two siblings have names associated with hunting terms.

The case is being turned over to the Atlantic County prosecutor's office because of a conflict of interest in the Ocean County prosecutor's office, law enforcement sources said.

The shooting has brought a new reality check for parents whose children go to play at neighbors' homes.

"My sister said she would actually ask, 'Do you have guns, are they locked up?' Because you never know today. You never know," said neighbor Debi Coto.

"I feel bad for the 4-year-old, because he's going to have to live with it," said Suppa. "He probably doesn't even understand it."