A four-year-old Woodbridge boy died Wednesday after he found a gun in a family member’s parked truck and shot himself in the head, Prince William County police said.

Authorities said that about 3:25 p.m., one of the boy’s relatives called police to report the shooting, which occurred outside a home in the 14800 block of Empire Street.

The child was taken to a hospital, where he was pronounced dead, police said.

The boy was alone when he got into an unlocked truck that was parked on the street, said Officer Jonathan Perok, a Prince William police spokesman.

Perok did not say which relative owned the truck or precisely where the handgun was located.

“This was a tragedy,” Perok said. “The family is grieving. We need to wait for them to calm down and do the investigation.”

Police would not immediately identify the boy, saying they were still working to contact family members. It was not clear whether the boy lived at the Empire Street home.

One woman outside the house said she was a family member but declined to give her name. “It wouldn’t have happened if I was there,” said the woman, who was visibly upset.

Timothy Frye, 50, a neighbor, said he heard a pop that was the gunshot but didn’t realize what it was. He said he often saw children playing near the home.

Perok said investigators were continuing to interview family members to determine where everyone was at the time of the shooting.