Around 9:30 Thursday evening, police responded to the teen's home on Cypress Avenue in Richboro, Bucks County.
When police arrived, the suspect's mother invited them in. They asked if she had guns in the house and she told them she had her grandfather's guns.
Located on the nightstand in the teenager's bedroom were two 9mm handguns. Police say the weapons were fully functional, but unloaded. One had a clip capacity of 8 - the other a capacity of 13 bullets. Also found in the bedroom was a non-functioning AK-47 replica.
Police say earlier that day, he told a classmate he planned an armed assault at school.
"Indicating that he was going to bring a gun and knives into the school Friday morning and randomly kill students and staff," said Chief Barry Pilla, Northampton Township Police.
The boy who heard the threat told his father, and he called the police.
In addition to the handguns, police found assorted knives, swords and machetes throughout the house.
Authorities arrested the 9th grader on charges of making terroristic threats and weapons offenses.
Also arrested was the boy's mother, 50-year-old Elizabeth Donohoe, charged with possession of a fire arm, endangering the welfare of children, possession of marijuana and possession of drug paraphernalia.
The suspect's father - 48-year-old Vincent Mario Russo Jr. of the 500 block of West Street Road in Feasterville was arrested as well, charged with obstruction of justice and resisting arrest.
Police continued to search the home Friday afternoon, finding more weapons. The teen suspect's name has not been released because he is a juvenile.
Classmates say, he was bullied because of odd behavior.
"He's kept to himself. He doesn't have many friends. I know kids make fun of him a lot because of how he looks," said Alex, student.
Meanwhile Council Rock High School South was closed Friday as police conducted a sweep for weapons but nothing was recovered.
There were also no classes today at Emmaus High School in Lehigh County due to a bomb threat.
School officials did not specify how it received the threat. Bomb sniffing dogs scanned the school property, but found nothing.
Families of Emmaus students received an automated message Thursday evening explaining the incident.
Officials said they believe the threat is not credible, but as a precaution all daytime and evening activities on Friday have been cancelled.
Chuck Ballard, East Penn School District Board President, said a criminal investigation is underway.
"Our number one goal now is to work with law enforcement to make sure our school is safe and secure, " said East Penn School District Superintendent Thomas L. Seidenberger.
The school also posted a note on their website.
Emmaus High School's head basketball coach said the boys varsity basketball game will be moved to Rockne Hall at Central Catholic.
Offices at the high school have also been closed. All other schools are in session on their normal schedules.