Who hits Myrtle with the car in Gatsby? Did Gatsby do it? Why was he killed?

Daisy runs Myrtle down because she knows she is Tom's mistress. Gatsby was in the penger seat, but only Daisy and Gatsby really know what happened, so when Wilson asks Tom whose car it is, he umes that Gatsby was driving... he kills Gatsby as revenge for his wife and their terrible marrage.