Nearly a month after a fertilizer company exploded in West, Texas, shockwaves of uncertainty surrounding the blast continue to reverberate—and the results of an exhaustive investigation by the Bureau of Alcohol, Tobacco, Firearms and Explosives has done little to quell them.

After a $1 million investigation that included more than 500 interviews, the ATF said Thursday that it could not rule out or confirm arson as a culprit in the explosion, according to Reuters. Other possible causes include the building’s electrical system and a potentially faulty golf cart.

“At this time, the State Fire Marshal’s Office and ATF are ruling the cause of the fire as undetermined,” the Washington Post quoted State Fire Marshal Chris Connealy as saying.

The ruling joins a long list of facts about the April 17 blast that are still undetermined, including whether or not paramedic Bryce Reed was involved. Reed, who responded to incident and eulogized at least one of the 10 responders killed fighting the fire, was arrested last week for allegedly possessing parts of a pipe bomb. Reed pleaded not guilty to the charges and denies having anything to do with the explosion, according to Reuters.

"We continue to ask our community to reserve judgment until the facts and evidence are known," Reed’s attorney Jonathan Sibley told Reuters.

Authorities have said they won’t yet speculate if Reed played a part in the blast, but they do know more about the actual explosion, which they posited was caused by something “impacting” a bin of ammonium nitrate that had become unstable in the heat of a fire. The result was a blast equal to 15,000 to 20,000 pounds of TNT, according to the Los Angeles Times.

Meanwhile, the explosion has dislodged a bevy of broad concerns ranging from possible lapses emergency planning to the lax regulatory climate of Texas to the need for stronger chemical plant security nationwide. The company, too, has come under scrutiny for frequent thefts of chemicals and remaining “willfully off the grid” when it came to reporting explosive fertilizer to federal agencies.

“This shows that the enforcement routine has to be more robust, on local, state and federal levels,” chemical standard safety expert, Sam Mannan, of Texas A&M University told Reuters. “If information is not shared with agencies, which appears to have happened here, then the regulations won't work.”