The investigation was announced Friday by the Texas Department of Public Safety, which oversees the Rangers.
"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," said Steven McCraw, the DPS director, in a news release. No further details were released.
Parnell McNamara, the sheriff of McLennan County, where the blast occurred, said in a statement that Texans "must have confidence that this incident has been looked at from every angle and professionally handled."
A call to the DPS public affairs office was not immediately returned.
The fire at the West fertilizer plant on April 17 was followed by explosion that killed at least 14 people.
Officials had originally said they hoped to complete their investigation of the West disaster by May 10. But the investigation is expected to take up to two weeks longer, according to the state fire marshal's office.
Also Friday, Sheriff McNamara said that the Bureau Alcohol Tobacco and Firearms amd Texas State Fire Marshall had arrested Bryce Reed, reportedly a paramedic in West, for possessing an explosive device, though whether this had any link to the blast is unclear.
"It is important to emphasize that at this point, no evidence has been uncovered to indicate any connection to the event surrounding the fire and subsequent explosion at the West Fertilizer Plant and the arrest of Bryce Reed by the A.T.F.," McNamara said in a press release Friday.
State Rep. Kyle Kacal, R-College Station, whose district includes West, said he received a call about the arrest at about 2 a.m. Friday after a long night on the House floor. He said he was unsure whether there was any connection between the investigation and the arrest.
"There is always a criminal investigation" after incidents like these, Kacal said. He added that he was glad that law enforcement reacted quickly with the arrest though it may not be related to the explosion investigation.
Reporter Julian Aguilar contributed to this report.
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This article originally appeared in The Texas Tribune at http://www.texastribune.org/2013/05/10/criminal-probe-launched-fertilizer-plant-blast/.