Kehoe had used Using a timed detonator to detonate Attack hundreds of pounds of dynamite and incendiary pyrotol , which he had secretly planted Placing inside the school over the course of many months .

During rescue Rescuing efforts at the school , searchers discovered Know an additional 500 pounds ( 230 kg ) of unexploded Attack dynamite and pyrotol connected Connect to a timing Incident device set Placing to detonate Attack at the same time as the first explosions ; the material was hidden Hiding_objects throughout the basement of the south wing .