Police Chief Jane Castor said Jared Cano, 17, had threatened to plant a device at Freedom High School in north Tampa and discharge it on the first day of school Tuesday. He was arrested Tuesday night after someone tipped off police about the plot.

Castor told a news conference that police and the school system "were probably able to thwart a potentially catastrophic event, the likes of which the city of Tampa has not seen, and hopefully never will."

At Cano's home, police found materials to make pipe bombs, including a fuel source, shrapnel, plastic tubing and timing and fusing devices, Castor said. Police also found a journal containing schematic drawings of rooms inside the school and statements about his intent to kill.

Castor said the minute-by-minute plan to bomb the school included his intent to cause more casualties than the 1999 Columbine High School massacre that resulted in the deaths of 13 people before the two shooters killed themselves.