What characters are morally responsible for Jay Gatsby's death? Even though George Wilson pulled the trigger, are other characters also responsible?

In The Great Gatsby by F. Scott Fitzgerald, George Wilson is quite understandably distraught over the death of his wife by a hit-and-run driver. However, he should bear full responsibility for the murder. No one forced him to shoot Gatsby, and he could have reported the incident to the police and let justice take its course. Even if he felt that justice is only for the rich and that the poor are ignored by the criminal justice system, murder is still a moral choice that he made freely.
Obviously, other people contributed to the preconditions of the murder of Gatsby. Daisy is guilty of manslaughter in the death of Myrtle, and she should have had the decency to admit as much to the police and suffer the penalties for it. Gatsby himself is guilty of covering up Myrtle's death, and Tom is guilty of lying to George and blaming Gatsby. Gatsby also could have avoided being murdered by following Nick's suggestion and leaving town until George calmed down. Ultimately, however, although other characters are blameworthy, Wilson did make a free choice to murder Gatsby.