LANCASTER, Calif. - Two teenagers were in custody for allegedly plotting to carry out a Columbine-like massacre at their former high school next Valentine's Day, authorities said. The former Quartz Hill High students, whose names were not released, were arrested Thursday after searches of their homes turned up knives, ammunition, a gas mask and bomb-making instructions downloaded from the Internet, according to the Los Angeles County Sheriff's Department. They were being held at the Sylmar Juvenile Detention Center for investigation of making terrorist threats, Brown said. "I've been working with schools for eight years, and we have hoaxes all the time, but this is the first time that I thought, 'Oops, this one could really happen,'" sheriff's Sgt. Darrel Brown said Friday. "You could see they were preparing meticulously, taking things step by step." The boys, ages 17 and 15, had been transferred from Quartz Hill to other schools for disciplinary reasons, authorities said. Brown said an investigation began Wednesday when a student contacted the school's vice principal and said the former classmates were planning a "Columbine-style assault" on the campus. The student said she had learned about it second-hand. The boys told investigators that they planned to kill Quartz Hill students who had made fun of them, using guns and homemade explosives, then commit suicide, Brown said. On Friday, deputies at the sheriff's station in Lancaster displayed a page from the 15-year-old's notebook with the scrawled message: "When I'm God, everyone dies." The notebook was accompanied by a three-ring binder with pictures of Columbine High School killers Eric Harris and Dylan Klebold, Oklahoma City bomber Timothy McVeigh and murderer Charles Manson. Deputies said they found a black trench coat at one boy's home, possibly to be used in imitation of the similarly-dressed Columbine killers, and the 15-year-old boy had carved the word "hate" into his forearm, authorities alleged.