Motive a mystery in fatal California school shooting

Parent Mirna Herrera kneels with her daughters Liliana, 15, and Alexandra, 16 at the Central Park memorial for the Saugus High School victims in Santa Clarita, Calif., Friday, Nov. 15, 2019. Investigators said Friday they have yet to find a diary, manifesto or note that would explain why a boy killed two students outside his Southern California high school on his 16th birthday. (AP Photo/Damian Dovarganes)

Los Angeles Sheriff Sheriff Alex Villanueva expresses his condolences for the victims of the shooting at Saugus High School at a news conference at the station Santa Clarita, Calif., Friday, Nov. 15, 2019. (AP Photo/Damian Dovarganes)

SANTA CLARITA, Calif. — A 16-year-old boy planned the attack that killed two students and wounded three others at a Southern California high school, but investigators so far are unable to find out why he brought a gun to campus and opened fire, authorities said Friday.