Seventeen Canadian residents were in custody Saturday on terrorism-related charges, including plots to use explosives in attacks on Canadian soil, authorities said. The Royal Canadian Mounted Police said they arrested 12 male adults and five youth and foiled plans for terrorist attacks against targets in southern Ontario. Officials showed evidence of bomb making materials, a computer hard drive, camouflage uniforms and what appears to be a door with bullet holes in it at a news conference Saturday morning. "This group took steps to acquire three tons of ammonium nitrate and other components necessary to create explosive devices," said assistant Royal Canadian Mounted Police commissioner Mike McDonell said. McDonell said that is three times the amount used to blow up the Murrah Federal Building in Oklahoma City. The arrests were made Friday, with some 400 officers involved. McDonell said the suspects were either citizens or residents of Canada and had trained together.