WACO, Texas (AP) — Texas law enforcement officials on Friday launched a criminal investigation into the massive fertilizer plant explosion that killed 14 people last month, after weeks of largely treating the blast as an industrial accident.

The announcement came the same day federal agents said they found bomb-making materials belonging to a paramedic who helped evacuate residents the night of the explosion. Bryce Reed was arrested early Friday on a charge of possessing a destructive device, but law enforcement officials said they had not linked the charge to the April 17 fire and blast at West Fertilizer Co.