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Los Angeles police badly miscalculated the amount of fireworks they placed into a containment vessel before detonating them and causing a massive explosion that destroyed part of a South L.A. neighborhood in June, according to a new report from federal investigators.

“It was caused by overloading the [total containment vessel] with more explosives than the TCV was designed for,” said Asst. Special Agent in Charge Michael Hoffman, of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, during a closed-door meeting with local residents Monday night. “That’s what caused the failure.”

Hoffman said the ATF had ruled out other causes for the explosion, such as degradation of the containment vessel over time or a malfunctioning of its door, and determined the “overloading” of the vessel was the sole cause for the blast that destroyed dozens of homes, cars and businesses.

Hoffman said the LAPD’s containment vehicle was designed to handle repeated detonations of 19 pounds of TNT equivalent at a time, or a single detonation of 33 pounds of explosives before being returned to its manufacturer for analysis.

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