Brother Mouzone tells Avon that money will not settle the debt and that Avon must give up Stringer in order to maintain his word and reputation and, thus, continue dealing with New York. Avon is forced to give up Stringer to appease Mouzone and maintain his business contact.

Why did Stringer Bell get killed?

Stringer at first tries desperately bargaining for his life, but when Omar reveals that he and Mouzone are after him for personal reasons, and that Avon has betrayed him, he sombrely resigns to his fate and is shot to death by Omar and Mouzone.

Who Killed Brother Mouzone?

Stringer was right, and not long after planting the lie in Omar's mind, Omar confronted Mouzone and shot him in the abdomen, severely wounding him.