An American Fork man has been arrested on suspicion of killing his infant son in what police call a murder-suicide attempt.

Joshua Petersen was booked Friday night into the Utah County Jail on a first-degree felony charge of aggravated murder. He's being held without bail.

The 21-year-old Petersen is accused of shooting his 5-month-old son Ryker in the head with a rifle. The baby was taken to the hospital, where he was pronounced dead.

Police say Petersen sought to turn the gun on himself after killing his son, but was stopped by a family member. Investigators were unsure of the motive for the Friday afternoon slaying.

Neighbors say an older couple lived in the home, along with adult children and grandchildren.