In The Great Gatsby, Wilson is most responsible for Gatsby's death--he pulls the trigger. He shoots Gatsby, and Gatsby dies.
Anyone else's role in the death is ancillary--related to the primary cause, but not the primary cause.
Tom and Daisy do wreak havoc by playing, so to speak, with others in the novel, and Tom tells Wilson that Gatsby owns the car that hit Myrtle. But Tom probably doesn't know Daisy was driving. When Nick meets Tom after the story is basically over, Nick concludes that Tom doesn't know. Though Nick may be an unreliable narrator, he errs, if he errs, against Tom, not in his favor. Nick is ripe to heap more blame on Tom. If there was a chance that Tom knows Daisy was the one actually driving, Nick would say it.
Daisy, as well, deserves blame. She could have told the truth. She should have told Tom and the police and everybody else that she was driving, but she doesn't.
Nick could have intervened as well. He knows the truth, but he doesn't say anything, either.
There's much blame to go around, but again, Wilson pulls the trigger.