Explain how Nick, Daisy, Tom, George, and Gatsby could be in some way responsible for the death of Gatsby

Tom alludes to the fact Myrtle was killed by Gatsby's car.

“Listen,” said Tom, shaking him a little. “I just got here a minute ago, from New York. 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.”

Daisy was the driver, she killed Myrtle and drove away without taking responsibility. 

“Was Daisy driving?”

“Yes,” he said after a moment, “but of course I’ll say I was. You see, when we left New York she was very nervous and she thought it would steady her to drive — and this woman rushed out at us just as we were passing a car coming the other way.

George pulled the trigger on Gatsby, and then himself.

It was after we started with Gatsby toward the house that the gardener saw Wilson’s body a little way off in the grass, and the holocaust was complete.