The deadly history of ammonium nitrate, the explosive linked to the Beirut blast. A deep-dive into the chemistry and legacy of the compound offers clues into what sparked Lebanon’s catastrophe.

The investigation began after a 911 call around 2:15 p.m. Oct. 10 that alerted police to an unmarked, locked, approximately 5-foot-by-5-foot steel box filled with suspected explosive materials at ...