TACOMA, Wash. -- A 22-year-old man was trying to break up a fight between his stepfather and mother when he was shot and killed at their home in Tacoma on Thursday night, police said.

The boy's mother called police Thursday night to report her son had been shot.

"We discovered a 22-year-old male inside the home who apparently had one single gunshot to the head," said Officer Tracy Conaway of the Tacoma Police Department. "He was transported to a local hospital and died within about 40 minutes after the incident."

Police spokesman Mark Fulghum said the man was trying to be the peacekeeper when he was shot in a struggle for the gun. Investigators are trying to determine if the shooting was accidental or intentional.

Police questioned the couple and booked the 53-year-old stepfather into jail early Friday for investigation of second-degree murder.