Tampa, Florida (CNN) -- A teen apprehended by police in Tampa, Florida, planned to set off explosives and kill dozens of students on the first day of classes at his former high school, authorities said Wednesday.

A tip led police to 17-year-old Jared Cano's home, Tampa Police Chief Jane Castor said. Investigators found explosive materials there and a manifesto that outlined a minute-by-minute plan and named specific targets at Freedom High School, Castor said.

Cano was a student there until he was expelled last year, school officials said.

He allegedly hoped to kill two assistant principals at the school and about 30 students, aiming to exceed the level of violence associated with the 1999 school shootings in Columbine, Colorado, Castor said.

"It would have been catastrophic," Castor told CNN.

She said the manifesto investigators found included detailed drawings about where bombs would be planted. Authorities also determined that Cano had materials to make and detonate pipe bombs, she alleged.

"His intent was to place these devices throughout the school, where they would do the most harm," she said.

Cano is charged with possessing bomb-making materials and threatening to throw, project, place or discharge a destructive device. He also faces drug charges.

The teenager has not spoken with investigators since his arrest Tuesday, Castor said.

Cano will be represented by a public defender, but a specific attorney has not been appointed, said Mike Peacock, administrative counsel for the Hillsborough County public defender's office.

"By policy and procedure we would not comment on a pending case," he said.

The principal of Freedom High School, where classes are scheduled to start Tuesday for the school's 2,100 students, said he was shocked when he learned about the evidence authorities had collected.

"We take every threat seriously, but 95% of the time it turns out that it's not real," Principal Chris Farkas told reporters.

"I'm not sure that his plot was realistic to carry out," he added.

But still, Farkas said word of the planned attack left members of the school's community shaken.

"You hear about things nationally, but I think that to have it here in your backyard ... shock is probably one of the first things (you feel), and then I think there's fear that goes along with it," he said.

Cano was expelled from Freedom High School in March 2010 after what Farkas described as an "off-campus incident."

Lewis Brinson, the Hillsborough County assistant superintendent for administration, said "inappropriate behavior" led to Cano's expulsion, but did not provide further details.

A Tampa Police report from the month Cano was expelled from school alleges that Cano stole a gun from a neighbor's house. When investigators later came to his door, he answered it holding an aluminum baseball bat "in an aggressive manner," the report said.

Castor said Wednesday that police dispatchers received a tip regarding Cano's alleged plans, though she declined to name the individual who called.

His arrest Tuesday was a "milestone" in the case, Castor said, but the investigation continues.

Authorities are looking into where the suspect acquired the explosive materials and whether he had any access to firearms, she said. On Wednesday they learned he had allegedly practiced setting off explosives in the past, she said, but declined to provide further details.

Authorities do not believe anyone else was involved in the alleged plot, Castor said.

She stressed that Cano's family has been cooperating with authorities and said there was no evidence the family was aware of the plan.

Evidence police collected suggests that Cano could have carried out the attack and "was very serious about it," Castor said, though she said it was impossible to say how successful he might have been.

Police have agreed to step up security for the first day of school -- scheduled for Tuesday -- "just to make people feel more safe," Farkas said.

The fact that a tipster led to the former student's arrest in Tampa shows the importance of schools nationwide building a relationship with their communities, said MaryEllen Elia, Hillsborough County Public Schools superintendent.

"Someone realized it was very important that they share this information and that they help us address this issue," she told CNN. "I think it's very important that we make sure that people are aware that this kind of situation could occur anywhere."

CNN's John Couwels, David Mattingly, Jason Morris, Catherine E. Shoichet and Brooke Baldwin contributed to this report.