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.
In The Great Gatsby, Daisy and Tom Buchanan are most responsible for Gatsby's death. The true villain of the narrative, Tom employs Daisy's idea of relieving their boredom by going to town and insidiously urges Gatsby to take Daisy in his coupe, allowing Gatsby to be seen with her. At the hotel in New York, Tom becomes combative with Gatsby and interrogates him about his business dealings and his past, calling him a racketeer and a swindler. When Gatsby rises to the challenge and urges Daisy to tell Tom that she does not love him, the air becomes charged with emotion as Daisy withdraws into herself. So, Tom, already knowing that Daisy is extremely unnerved, instructs his wife to take Gatsby's car and head back to East Egg. When Tom espies the accident, he stops to ascertain what has happened; and, although he has been witness to the mettle of Gatsby, he desires to assume that Gatsby has struck and killed Myrtle, and has, with cowardice, driven on.
As the chivalrous Gatsby watches outside the Buchanan house, concerned for Daisy, the nefarious Tom conspires with his pusillanimous wife. And, he obviously persuades her to implicate Gatsby in the death of Myrtle Wilson. So, while she lacks the fortitude to be honest about what has happened, Tom Buchanan is villainous in his coersion of his wife and betrayal of Gatsby. It if were not for Tom Buchanan's plan of implicating Gatsby as the driver of the "yellow death car," Wilson would have sought out the driver and not killed Gatsby.