By venturing beyond the deaths of American Presidents, O'Reilly opens the door to the possibility of a broader range of historic figures for future tomes. Might we see Killing Socrates? Killing Gandhi? Killing Lennon? Personally, I'm rooting for Killing Caesar to be the next volume, with a dramatic retelling of the murder of Julius Caesar.
The Killing series has become an enormously successful franchise. The television adaptation that aired on the National Geographic Channel drew an incredibly large audience. (It's queued up on my DVR, waiting for me to watch it.)
Mr. O'Reilly certainly doesn't need our cash to make him any richer, but this is a page-turning series as each book takes a tragic event that altered the course of human history and retells it in dramatic, gripping fashion, as if the reader was learning about it for the first time.