Castor credited police and an "informant" - a high school student whom the teenager tried to recruit - for averting a potential disaster.
The teenager had no ammunition for the weapon, and Castor said there was no evidence an attack was imminent, but, nevertheless, fear gripped the high school after parents and students learned of the possible plot between 9:45 a.m. yesterday, when the school sent out 4,700 automated messages, and 10:45, when teachers made an announcement.
Although the school message emphasized that students were not in danger, many parents were not convinced. Within minutes the campus - already flooded with police cars and officers - became even more congested as parents arrived to pick up their children.
"It's pandemonium," said Maureen Bickings, the mother of Jamie Bickings, 15, and a resident of Plymouth Meeting. "They can't assure us he worked alone. . . . I think my daughter is safer at home."
"He has to have backup at our school; it can't just be one person," said student Ashley Foley, 15.
Castor said it was the 14-year-old's attempt to recruit assistance that led to his apprehension Wednesday night. The boy he contacted informed his parents, who then alerted police.
"They're to be commended," said Castor.
Plymouth Township Police Chief Carmen D. Pettine said the incident was particularly disturbing "after what happened in Ohio." A day earlier, a 14-year-old in Cleveland shot four people at a high school there, and then killed himself.
School officials from the Colonial School District, which serves Plymouth and Whitemarsh Townships and Conshohocken Borough, declined to discuss their decision to keep the school open, or what security will be in place today. David Sherman, the district's community relations coordinator, referred questions to Castor, who said security would be stepped up.
Counselors will be available at the school today, officials said, and principal Monica Sullivan will address students about the incident.
Citing privacy laws, Castor declined to name the local juvenile or his family, though many students and neighbors believe they know the teenager's identity. Castor said he expected to make a decision within the next few days on whether to charge the teen as an adult. The teenager is in custody of juvenile authorities pending a court hearing.
Castor is also considering whether to file charges against the boy's parents.
Castor said the mother legally purchased the 9mm semiautomatic (which had a laser sight) at a gun show, but then gave it to the teenager, which is a potential violation of state law. He noted that the other items seized from the boy's room were in plain sight. "There is no way that one or both parents doesn't know this," Castor said.
The other items included 30 knives and other edged weapons, and the host of BB guns, designed to resemble genuine assault rifles and automatic weapons.
Police also seized DVDs of the Columbine shooting, notebooks detailing acts of violence, a hand-painted Nazi flag, and books such as The Anarchist Cookbook and a U.S. Army counterinsurgency operations handbook.
Castor said the youth, whose possessions suggested "a disturbed mind," had attended Plymouth schools until his parents started home-schooling him because he was being bullied by other students.
In front of the alarming display of BB guns and knives presented to the media, Castor added that it was difficult to ascertain exactly what acts the teenager might have been willing to undertake.
It could have simply been "big-talking by a student who thought he was bullied previously," Castor said.
On his MySpace site, the student listed his favorite weapons, deeming the AK-47 his top choice. The site is replete with references to Eric Harris and Dylan Klebold, and says one of his interests is their 1999 massacre in Columbine High School.
He sought to meet "chicks" or "followers willing to be my soldiers." His motto: "Mess with the best, Die like the rest."
"I am pretymuch," he wrote in a badly spelled post, "the posterboy for the person that rests upon the line between Geineus and Madman/Pycopath." The teenager last logged on in early September.
No one answered the door at the teenager's Plymouth Meeting ranch-style home, where a collection of wind chimes lining the front porch blew in the breeze along with an American flag and an Eagles banner. An earlier visitor had left a bouquet of fresh flowers and an envelope.
Beverly Ingram, who lives a couple of doors away, said her grandchildren used to love to play with the teenager five or six years ago.
"He had a menagerie: rabbits, ducks, a dog," she said. "He had everything; his parents got him whatever he wanted."
Ingram, who said she hadn't interacted with the youth in a couple of years, but said she had "thought he was the nicest kid," she said. "I'm totally amazed."
Another couple, who declined to be named, said they often saw the boy shooting BB guns in the backyard.
Across the street, neighbor Eric Olsen kept shaking his head, chilled by the close proximity of the weapons to his 7-month-old daughter.
"To me, he seemed like a normal kid," Olsen said. "I feel for the parents; I hope he gets the help he needs."
Contact staff writer Kathleen Brady Shea at 610-701-7625 or firstname.lastname@example.org.
Inquirer staff writer Dan Hardy contributed to this article.
For more information on the school district, videos and links for anti-bullying programs and advice, go to http://go.philly.com/bullying