TAMPA, Fla. (AP) — Police in Tampa, Fla., say the 17-year-old who’s accused of plotting to set off a bomb at his former high school had prepared a minute-by-minute plan — along with schematic drawings of rooms inside the school.

Jared Cano was arrested last night after someone tipped off police about the plot targeting the school, where he’d been expelled.

Police say it could have been a “catastrophic” event. They say it was planned for next Tuesday, the first day of school.

They say the found materials at his home with which to make pipe bombs — including shrapnel and plastic tubing. According to Tampa’s police chief, the detailed plan spelled out Cano’s intent to cause more casualties than the 1999 Columbine High School attack that killed 13 people before the two shooters killed themselves.

Cano has had multiple juvenile arrests. Police say he’d been on a list of juveniles they checked on from time to time.

According to the St. Petersburg Times, prosecutors said in court this morning that when he was arrested, Cano repeated his plan to bomb the school and cause mass casualties. The paper says he started to speak in court today, but was stopped by a public defender.