"“You could smell the smoke and you could hear things falling like through the vents,” he said. “It just smelled like sulfur.”"
Potassium chlorate
"Sulfur should be avoided in pyrotechnic compositions containing potassium chlorate, as these mixtures are prone to spontaneous deflagration."
Someone murdered Todd and planted an explosive designed to create a massive fire very quickly to hide evidence of what occurred and possibly burn down a good chunk of the building.. However the building withstood the deflagration. Most evidence would be toast.