He owed a large debt and somebody decided to make him pay. This was a methodical killing in which the assailants took their time. The GS9 are known for their overt shootings and a few quiet ones. They chose to go through the cement shoes tactic when it's obviously they could of execution style via headshot. A quiet route probably meant serious business and perhaps a rival group ( Folks Nation/GDs, etc) is responsible for his death.