What is concluded about Wilson's motive for killing Gatsby?
When Gatsby is killed by Wilson, everyone assumes it is because Gatsby had run over his wife, Myrtle, with his car. In actuality, Daisy was the one who was driving, but Gatsby took the blame for it. Myrtle's sister, Catherine, concluded that the death of her sister, Myrtle, had caused Myrtle's husband, George Wilson, to go crazy and kill Gatsby out of derangement:
...but Catherine, who might have said anything, didn’t say a word. She showed a surprising amount of character about it too—looked at the coroner with determined eyes under that corrected brow of hers, and swore that her sister had never seen Gatsby, that her sister was completely happy with her husband, that her sister had been into no mischief whatever. She convinced herself of it, and cried into her handkerchief, as if the very suggestion was more than she could endure. So Wilson was reduced to a man “deranged by grief.” in order that the case might remain in its simplist form. And it rested there.
At the end of the novel, Nick runs into Tom while walking down the street in New York. Nick refuses to shake hands with Tom, thinking that Tom has known all along that it was Daisy that had been driving the car, not Gatsby. He has suspected for years that it was Tom who told Wilson that the car that hit his wife, Myrtle, belonged to Gatsby. Tom tells Nick that Gatsby got what he deserved.
He ran over Myrtle like you’d run over a dog and never even stopped his car.”
Nick knows that this is not true. He concludes that Tom and Daisy "were careless people."
Read about the novel here on enotes.