Two teenagers meticulously planned an attack on their high school this year but were arrested before they could carry it out, according to a published report.

Johnny Alvarez Casas, 17 at the time, and a 15-year-old friend stockpiled ammunition and bomb-making materials, then practiced detonating improvised explosives in the desert in anticipation of a February attack, sheriff's deputies told a newspaper for a story Saturday.

The younger suspect's name was withheld because of his age.

The plot on Quartz Hill High School, north of Los Angeles, unraveled when a 16-year-old sophomore heard the boys were planning to cut off her arms and legs during the attack and alerted an assistant principal, deputies said. The boys were arrested Dec. 15.

"This was the first time I saw so much evidence and planning that led me to believe that something would actually happen," said Sgt. Darrell Brown of the Lancaster sheriff's station.

James A. Stevens, Casas' defense attorney, said authorities used a "good cop, bad cop" routine to get a false confession. The suspects, who are charged with conspiracy to commit murder, have pleaded not guilty. A judge has ruled that Casas should be tried as an adult.

Deputies said the boys confessed that they planned the attack as retaliation for ridicule.

Stevens said authorities were overreacting out of fear of a repeat of the 1999 attack on Columbine High School in Littleton, Colorado, in which two teenage boys killed 12 students and a teacher before turning their guns on themselves.

He said Casas was a harmless, confused kid of below-average intelligence shaken by his parents' divorce.

If convicted, Casas, now 18, faces up to life in prison without parole. His suspected accomplice, now 16, could be held in juvenile custody until he turns 25.

Five teenagers were arrested April 20, the seventh anniversary of the Columbine shootings, on charges of plotting a rampage at their high school in southeastern Kansas. Authorities say similar plots were being discussed in Alaska, Mississippi and Washington state.