I need help creating a thesis for the following topic. Who is morally responsible for Gatsby's death? The obvious answer is George Wilson because he pulled the trigger, but who are three characters who contributed in another way or could have prevented what happened?

After George Wilson, the next obvious choice is probably Daisy Buchanan. Daisy was driving the car which hit and killed Myrtle, but she takes advantage of Gatsby’s feelings for her and lets him take the blame. If she had confessed straight away, then George would not have shot Gatsby in the mistaken belief that it was Gatsby who killed Myrtle. Daisy's cowardice leads directly to Gatsby's death.
Tom Buchanan might also share some of the blame for Gatsby’s death. He tells George that Gatsby is the owner of the yellow “death car” which hit Myrtle, and, when questioned by Nick, he simply says that Gatsby “had it coming to him.” This quotation suggests that Tom told Wilson not out of any sense of duty or concern for justice, but because he disliked Gatsby and wanted to see Gatsby suffer. Tom also says to Nick that when George came to speak to him, George “was crazy enough to kill [him].” He must have known, therefore, that George was also crazy enough to kill Gatsby. But still, Tom gave Gatsby’s name to George. Tom is thus, at least to some extent, morally responsible for Gatsby’s death. The degree of his responsibility depends largely on whether or not he knew that Daisy, not Gatsby, was driving the car that hit Myrtle. If he knew that Daisy was driving and still gave Gatsby’s name to George, then Tom must be considered largely responsible.
Toward the end of chapter 7, after Myrtle’s death, Tom and Daisy are depicted “sitting opposite each other at the kitchen table.” Fitzgerald writes that there was “an unmistakable air of natural intimacy about the picture” and that anybody who could have seen them would have said that “they were conspiring together.” The word “conspiring” here implies that perhaps Tom did know that Daisy was driving; perhaps they both, at this moment, conspired to blame Gatsby for Myrtle's death. If this inference is correct, then Tom and Daisy together are both morally responsible for Gatsby’s death.
The third character who might be considered morally responsible for Gatsby’s death is Gatsby himself. His love for Daisy arguably renders him morally corrupt. He desperately chases wealth and status to convince her that he is good enough for her, and this desperation leads him into a world of crime, selling counterfeit bonds and bootlegged alcohol. It is also, arguably, morally corrupt of Gatsby not to turn himself and Daisy in to the authorities after Myrtle’s death. They both act out of selfishness: Daisy to preserve her freedom and Gatsby to preserve the love, or at least a faint hope of the love, he so desperately wants from Daisy. If not for this selfishness, justice could have taken its proper course, and George would have had no need to take justice into his own hands.