Who Killed Che Guevara?

I’m still not completely sure about the circumstances surrounding Che’s death, as I have not been here to watch most of the documentary. From what I gather, there were many people who could have potentially wanted him gone. From what I have watched so far, Castro seems to be a likely person to blame. However I also think that the United States may have been involved. As of now, I really don't feel like I know enough to be answering this particular question. Perhaps once I watch the documentary I will be able to form a more informed opinion.