WACO, Texas — 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 that a paramedic who helped to evacuate residents the night of the explosion was arrested on a charge of possessing a destructive device, though it is not clear whether the charge is related to the April 17 blast at West Fertilizer Co.

The Texas Department of Public Safety said in a Friday statement that the agency had instructed the Texas Rangers and the McLennan County Sheriff’s Department to conduct a criminal probe into the explosion.

“This disaster has severely impacted the community of West, and we want to ensure that no stone goes unturned and that all the facts related to this incident are uncovered,” DPS Director Steven McCraw said.

McLennan County Sheriff Parnell McNamara said residents “must have confidence that this incident has been looked at from every angle and professionally handled — they deserve nothing less.”

The statement did not detail any further reasons for the criminal investigation and said no additional information would be released.