WEST, Texas -- The cause of the explosion at the West Fertilizer Co. that killed 15 people remains undetermined despite a month-long, $1 million investigation, state and federal officials said Thursday.
State Fire Marshal Chris Connealy said investigators have narrowed the cause to one of three things: a shorted 120-volt electrical system, a defunct golf cart or an intentionally-set fire.
Officials said the electrical system and golf cart could not be ruled out because too many pieces are missing to prove that they didn't cause the fire, which set off two explosions "milliseconds" apart.
Authorities declined to speculate on whether the arrest of former West EMT Bryce Reed was related to the explosion. Reed was arrested on May 10 on a charge of possession of a destructive device. They said they wouldn't take any questions regarding Reed, citing the ongoing investigation.
Reed has pleaded not guilty to possessing an unregistered firearm and has vehemently denied being involved in the fertilizer plant explosion.
"We want to understand what happened to give closure to these families [of the victims,]" Marshal Connealy said.
The fire began in the seed room, which backed up to an ammonium nitrate storage bin. The golf cart was located in that room. Officials said the heat from the fire in the seed room caused the ammonium nitrate to be susceptible to shock. Falling debris hit the storage bin, which set off the first explosion and the larger second one.
Only 28 to 34 tons of the ammonium nitrate of the 150 total tons on the site exploded. The force of that amount was equal to 15,000 to 20,000 pounds of dynamite exploding, according to a spokesman with the Bureau of Alcohol, Tobacco and Firerarms. It left a crater 10 feet deep and 93 feet wide.
The attorney for the West Fertilizer company, John McCoy, said in a statement Thursday they thank the many enforcement agencies involved in the investigation, but had not further details to release.
"Out of respect to the various agencies and to assure that their investigations are not compromised, we will not offer any additional comments or opinions at this time," McCoy wrote. "Our thoughts and prayers continue to be with the families and friends of those lost in this tragedy."
In its mandatory Tier II report, the West Fertilizer Co. reported having 250 tons of ammonium nitrate onsite. Investigators found evidence of only 150, the ATF spokesman said.
Marshal Connealy said agents met earlier Thursday with the families of the victims of the explosion. He said he explained that the undetermined cause of the fire may be the best explanation they can give at the end of the investigation, but it is ongoing and they will leave "no stone unturned."
Some family members that spoke with News 8 said they understand the investigation is complicated but they wish there were more answers.
"I lost a son," said Bill Uptmor.
His son Buck rushed to help that April 17 night and was a well-known presence at the local fire department.
ATF investigators said the excavation of the blast site is complete and 280 leads have been followed. More than 400 people have been interviewed, 250 pieces of evidence have been collected and the ATF has spent more than $1 million on the investigation.
Investigators have used forensic mapping, chemical analysis, computer modeling and reconstruction of key components of the blast in their investigation.
The explosions killed 15 people, including 12 first responders.
"[It was] certainly one of the worst [events] in American history [in terms of] first responder [deaths]," Marshal Connealy said.
Governor Rick Perry said in a statement Thursday the explosion would forever leave a mark on the town, but the reaction from every state and federal and federal agency involved in the investigation is appreciated.
"While the cause of the fire remains undetermined and the investigation continues, this tragedy has shown the world the definition of compassion, from volunteer firefighters across the state rushing to help their colleagues at the scene, to friends, neighbors and Texans stepping in to help those who lost so much in the blast," Perry wrote.
U.S. Senators from Texas Ted Cruz and John Cornyn also released a joint statement Thursday afternoon, which said in part, "While the cause remains undetermined, it is our sincere hope that at the end of the investigation, the residents of West can find closure and begin to heal."