SYLMAR – A third teenager has been charged in connection with an alleged plot to stage a Columbine-style attack on Valentine’s Day at Quartz Hill High School, prosecutors said. The 16-year-old Quartz Hill High student, who officials said is a friend of the two boys already charged in the case, made threats to two students during a Jan. 28 telephone call, saying that he wanted carry out his friends’ alleged plot, officials said. “He made threats that he wanted to join the other two and continue their plot to kill students at Quartz Hill High School. He knew them and knew of their plot and said he wanted to join in,” Deputy District Attorney Ron Smalstig said. The boy also threatened to kill his parents, prosecutors said. In announcing the boys’ arrests in December, deputies said the teens had acquired bomb-making instructions off the Internet and detonated practice bombs in the desert. The two boys arrested in December had been on probation in connection with a 2003 assault in which a 14-year-old boy was sodomized with a metal rod, deputies said. The teens had attended Quartz Hill High School but were transferred in the fall to other schools because of past discipline problems. The 16-year-old enrolled at Desert Sands Charter School and the older boy at Littlerock High School. The investigation started when a girl contacted a Quartz Hill High vice principal and said she had been told by friends that the 16-year-old did not like her and was planning to kidnap and torture her and cut off her arms and legs. Karen Maeshiro, (661) 267-5744 [email protected] 160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set! AD Quality Auto 360p 720p 1080p Top articles1/5READ MORESanta Anita opens winter meet Saturday with loaded card The boy appeared in Sylmar Juvenile Court on Friday to be arraigned on five counts of making criminal threats against his parents, the two students he talked to on the telephone and Quartz Hill High School students in general. Sheriff’s deputies were notified of the telephone call threats and took the boy into custody earlier in the week, prosecutors said. The boy’s name was not being released because of his age. He lives with his parents in Lancaster. The alleged threats occurred during a telephone call while the boy was visiting relatives in another part of California, authorities said. The other two boys, ages 16 and 17, have denied conspiracy to commit murder charges. The younger boy also has denied a charge of making criminal threats. Prosecutors are seeking to try them as adults. The boys, who sheriff’s deputies said dressed in the Goth style, characterized by black clothing and nail polish, said they felt ostracized at Quartz Hill High and wanted to get revenge, deputies said.