Cops said firearms were found at the 17-year-old's home, but the guns were registered to his father.
Students are set to return to Bridgewater-Raritan High School this morning, days after a bomb scare shut down the campus.
A second teenager has been arrested in connection with the investigation of the planned attack at the school.
Somerset County Prosecutor Wayne J. Forrest said cops were led to a friend of the 16-year-old Bridgewater-Raritan High School student who was previously arrested. The suspect can only be identified as a 17-year-old boy who lives in Bridgewater and is a senior at Immaculata High School in Somerville.
Police conducted a search of the teenager's residence and discovered a number of firearms and shotgun shells that matched the shotgun shells that were previously seized from the 16-year-old's home.
The older boy is a competitive rifle shooter and the firearms that were located in his home were registered to his father, cops said.
Police later determined that the 17-year-old provided the shotgun shells to the 16-year-old for the purpose of constructing Improvised Explosive Devices (I.E.D.). Cops also say the older boy drove the younger one to the Home Depot in Bridgewater, N.J., where they purchased PVC piping, wiring, light sockets and light bulbs to make the explosive devices. After that, they prepared diagrams on how to assemble the devices and began doing so. The partially constructed devices were seized at the 16-year-old's home once cops got wind of the plan.
At the request of the school authorities at the Immaculata High School, a search utilizing bomb and explosive detecting dogs will be conducted prior to students returning to school on Monday morning.