Kentucky ? Human error – bringing a torch near a poorly built protective seal – sparked an explosion in an eastern Kentucky coal mine that killed five men, state investigators conclude in a report released Friday.

But after months of interviews and sifting through evidence, state officials still don’t know who authorized the use of the torch in the first place, or why.

The protective seal, which should have blocked out naturally occurring methane, was “poorly constructed” and failed to meet federal guidelines, according to an investigation report released by the state Office of Mine Safety and Licensing.