Sources say an investigation into the fatal April 17 blast at a West, Texas fertilizer plant has already yielded some information, though it’s expected to continue beyond this week.

The Texas State Fire Marshal’s Office has identified ammonium nitrate – a relatively inexpensive fertilizer with a high nitrogen content – as the substance that caused the explosion, killing 14 people and injuring approximately 200 more. Dozens of buildings near the site were destroyed or damaged.

A spokesman for the office said that in addition to that finding, investigators have been able to determine that the blast originated in the fertilizer and seed building – but not why it occurred. An ignition source has not yet been discovered.

In addition to its use as a fertilizer, ammonium nitrate is a component in a popular explosive. It was used as an ingredient in the Oklahoma City bombing in 1995 that left 168 people dead – one reason why facilities who store it in certain quantities are required to report that to the Department of Homeland Security. The West Fertilizer Co., owner and operator of the fertilizer plant, reportedly had not made that required report.

The Texas Department of Insurance (TDI), working in conjunction with other agencies, is providing assistance through the State Fire Marshal’s Office (SFMO), its Consumer Protection resources, and the Division of Workers’ Compensation (DWC) to assist those affected by the incident.

"We extend our condolences to the families of those killed or injured in the explosion," said Commissioner of Insurance Eleanor Kitzman and Commissioner of Workers’ Compensation Rod Bordelon, in a joint statement. "TDI and DWC are utilizing the full resources of the agency to assist those affected by this terrible event."