I find it very hard to believe that he had the ability to figure the system out but failed to even contemplate that he was leaving a rock solid breadcrumb trail behind.
I think he had either been setup by someone using his credentials and backdoors on his computer or more likely he was given the information by pro's who would take a cut of the money in whatever untraceable form later down the line. He may have even just purchased the information from one of the many darknet marketplaces.