The investigation into what caused SpaceX’s Falcon 9 rocket explosion in September has been a slow, careful process, but all parties involved seem to be finally closing in on a clear reason for what went wrong.

The culprit: an operational error in the fueling procedures for the rocket as it sat on the launchpad that fateful morning, awaiting a routine ignition test before its scheduled flight a few days later. That might actually be the best-case-scenario for SpaceX CEO Elon Musk and his team.

For weeks, speculation behind what happened ranged as wildly as UFOs and intentional sabotage, to more mundane causes, like manufacturing issues. The only thing known for sure is that there was a large breach in one of the parts of the second stage liquid oxygen tank.

That the problem may have been a human error first reported by The Wall Street Journal — would shift the blame away from the manufacturers of Falcon 9’s parts, and instead place it on personnel involved with the preflight launchpad tests.

SpaceX has not yet confirmed or denied these reports: The company’s official line is that its waiting for the investigation to deliver its final conclusions before publicly announcing what it thinks happened.

An operational error would actually be great news for SpaceX. Falcon 9 is the company’s flagship booster for conducting low Earth orbit launches. Any hardware flaw would cause it to overhaul the rocket’s design, reset the new rocket, and push back operations for several more months past an optimistic target to return to flight by November.

And of course, that work might cause the company to shift resources away from its future missions to Mars, which are supposed to occur in 2018, using the more-powerful Falcon Heavy booster.

If these reports turn out to be true, it would help to bring a close to SpaceX’s highest profile failure since the 2015 catastrophe, in which the Falcon 9 rocket, bound for the ISS, exploded mid-flight. With more than $10 billion in contracts, SpaceX can’t really afford to piss off any other customers.

Photos via US Launch Report