Authorities describe the threats as "Columbine-like," to hurt students and teachers at the Hawthorne Brook Middle School in Townsend.
Massachusetts Attorney General Tom Reilly told CBS This Morning Senior Correspondent Hattie Kauffman that the paralyzed teen made the threats in recent days through an America Online chat group, which dozens of eighth-graders from the school frequented.
"It was pretty badit started with just child pornography but took a very ugly turn the last week with explicit threats of physical harm to children and school administrators," Reilly said. "It was terrifying and points out the danger of this type of cyber-terrorism that the psychological damage that it did to parents and children to, and to an entire community and the terrible distraction of a school."
Reilly said it has left students, parents and teachers at the school shaken. The threats included a list of teachers and students to be targeted.
The suspect, whom authorities refused to name because he had not been charged as of Sunday, had been communicating with students since September using the chat group and several different aliases, Reilly said. The students gained access to the chat group from their homes.
Believing the older teen was a peer, the Townsend students included him in their conversations, revealing information about their town, their school and themselves, Reilly said.
But when the 19-year-old allegedly directed some students to Web sites that contained child pornography, some frightened children told their parents, who then called police.
On Thursday, school officials notified the parents of Hawthorne Brook Middle School's 650 students about the threats and held an assembly to calm students' fears. Bomb-sniffing dogs were brought into the building, and students' bags and backpacks were searched.
On Friday, authorities from Massachusetts and Missouri converged on the suspect's home, where he lives with his parents. It wasn't immediately clear how the 19-year-old, who was paralyzed from the neck down during a car crash in high school, used a computer.
After police confiscated the teen's computer equipment, he admitted to communicating with the students.
"This was no prank at all. It was very serious business," Reilly explained. "We had no idea whether or not this was realthere was never real danger of physical danger, but we didn't know that and the parents or school authorities didn't know that. We need some better laws and protection for kids and schools and parents in these situations."
"The message is be careful," Reilly said. "It's an incredible tool, the Internet. We want them to use it but be careful. When something inappropriate happens, and this really got out of control, tell your parnts. This was kids working with their parents and working with adults. As a result, we were able to jump on it and get it over with pretty quickly."
It's still unclear whether the suspect will be prosecuted in Massachusetts or Missouri.