The announcement came the same day 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.
"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 at this time.
Paramedic Bryce Reed, meanwhile, was in federal custody following his arrest on the charge of possessing a destructive device. Reed was booked into the McLennan County Jail at 2:40 a.m. and released before 8 a.m. to agents from the Bureau of Tobacco, Firearms and Explosives, according to McLennan County Jail booking clerk Brandy Gann.
Reed made an initial court appearance in federal court in Waco on Friday, but did not enter a plea. Assistant U.S. Attorney Mark Frazier would not release further details.
Officials have largely treated the explosion as an industrial accident, though investigators still searching for the cause of a fire that preceded the blast have said they would treat the area as a crime scene until all possibilities were considered. Authorities have focused on ammonium nitrate, a chemical commonly used as a fertilizer, but that also can be explosive in the right conditions, as the cause of the blast.
Reed was one of several paramedics who helped evacuate residents from nearby apartments after the fire erupted and shortly before the explosion. He has spoken to The Associated Press extensively, and said he was devastated by the explosion, which killed one of his closest friends, Cyrus Reed. The two are not related.
Bryce Reed's wife, Brittany Reed, declined to comment early Friday.
"I can't. No comment, no comment no comment right now," she said before hanging up the phone.
Plushnick-Masti reported from Houston. She can be followed on Twitter at https://twitter.com/RamitMastiAP
Copyright 2013 The Associated Press.