Early in the last afternoon of Myrtle Wilson's life, two cars pass the Wilson garage on the way to New York City. Daisy and Gatsby speed past the garage riding in the Buchanan's blue coupe. Tom, Nick, and Jordan stop at Wilson's garage to buy some gasoline for the car they were using, Gatsby's yellow car. Tom leads Wilson to believe the yellow car belongs to him. "'How do you like this one?"' inquired Tom. 'I bought it last week.' 'It's a nice yellow one,' said Wilson, as he strained at the handle."
Later that night, when George learns that a yellow car was "the death car," he assumes that Tom must have been at the wheel and therefore responsible for Myrtle's death. Tom makes sure George and the police understand that the yellow car was not his.
"I was bringing you that coupe we've been talking about. That yellow car I was driving this afternoon wasn't mine - do you hear? I haven't seen it all afternoon."
As the police investigate and find the dog-leash among Myrtle's belongings, George jumps to conclusions and assumes Tom had lied to him, that he was actually the owner and driver of the yellow car. When George disappears in the late afternoon, he makes his way to the Buchanan mansion to confront Tom. Tom, who doesn't know that Daisy was driving the car at the time it hit Myrtle, tells George that the yellow car's owner and driver was Gatsby.
I told him the truth...He was crazy enough to kill me if I hadn't told him who owned the car. His hand was on a revolver in his pocket every minute he was in the house-