reporter: tonight, a quick-thinking teen is being hailed as a hero for preventing a possible shooting at this school near pittsburgh. >> had they not reported this, there could've been a major catastrophe today at uniontown high school. >> reporter: the teen, overhearing a 14-year-old classmate on the bus, allegedly talking about plans to shoot four students today at uniontown high school in pennsylvania, recording the conversation and contacting police. >> that student overheard it and took appropriate action right on the bus. >> reporter: within hours, police searching the suspect's bedroom, finding an arsenal of weapons. three rifles, including a semi-automatic, a shotgun, two machetes, throwing knives, a revolver, a crossbow and ammunition for it all. other students posting these videos, extra security measures causing crowding outside the school. the principal keeping them updated. >> as a result of the investigation, the student was apprehended. >> reporter: the alleged motive? >> he just didn't like them. that's what he said. he didn't like them.