But there is a problem: The opposition itself, not Mr. Maduro’s men, appears to have set the cargo alight accidentally.

Unpublished footage obtained by The New York Times and previously released tapes — including footage released by the Colombian government, which has blamed Mr. Maduro for the fire — allowed for a reconstruction of the incident. It suggests that a Molotov cocktail thrown by an antigovernment protester was the most likely trigger for the blaze.

At one point, a homemade bomb made from a bottle is hurled toward the police, who were blocking a bridge connecting Colombia and Venezuela to prevent the aid trucks from getting through.

But the rag used to light the Molotov cocktail separates from the bottle, flying toward the aid truck instead.

Half a minute later, that truck is in flames.