The mayor of Saint John, N.B., says an alleged plot by three teenagers to launch a murderous attack on a local high school is "a wake-up call" for all of Canada.

Mayor Norm McFarlane told Canada AM his community is "in shock" at the news that the boys have been charged with planning the attack.

Details about the alleged plot to take over Saint John High, the oldest public high school in the country, are still emerging. But it appears the boys planned to systematically murder some of the staff and students.

Police arrested the thre earlier this week after the school's principal was tipped off about the plan.

The boys are aged 15 to 17 and are all local air cadets.

Apparently some other cadets heard the boys discussing the alleged plot during a March Break trip to Quebec City. The boys' alleged plot was reported to the principal of Saint John High on Monday, and shortly afterwards, the three were arrested.

McFarlane says the willingness of some people to come forward says a lot about the strength of his city.

"I think it shows a community that is very close-knit," he told Canada AM. "And, maybe, in a large community this would have happened because there wouldn't have been the same opportunity and the same feelings as these students had to go to the proper authorities."

At a bail hearing, police revealed the attack was planned for April 20 next year. The same day as the seventh anniversary of the 1999 shooting rampage by two students at Columbine High School in Colorado, in which 13 people died.

Although no weapons have been found in the Saint John plot, police did find gunpowder and other materials for making pipe bombs.

The National Post reported Friday that, in addition to being charged in Saint John, the same three boys are also being investigated by military police for a separate, undisclosed, incident in Quebec City.

At a bail hearing on Wednesday, police said the boys were planning to attack administration offices in the school with explosives, and that they were planning to kill the principal and other officials with guns and bombs.

The allegations went on to say that the boys then wanted to work from a list they'd created of "hated" students, and that they would order them into offices and execute them one by one.

The three teens can't be named because they've been charged as young offenders.

They've been placed under house arrest and suspended both from school and from the cadets.

McFarlane says Saint John already feels it has learned a lot from all of this.

"I think out of something like this there always comes an opportunity. And I think there's an opportunity for people across the country to look into their own areas."

McFarlane also suggested parents should be mindful of what kind of websites their children are visiting.

"Parents must be very conscious of their children when they're on the Internet -- when they're looking at what sites," he said.

"You can actually get recipes to make bombs and so on, so we must be diligent."

The mayor also said the alleged plot is a wake up call for parents to take bullying at school seriously.

"Children today have so much in front of them, we must look at it," McFarlane said.