I have long had a suspicion that Yoko was in on it with Chapman.....Was John on the verge of leaving her? Was John having a change of heart, politically at the time? Who stood to gain the most from his death?
I don’t have any proof, but the fact Chapman spared her, does raise some of those questions.
I’d say there was a simpler reason: Chapman didn’t have silver bullets, garlic, or a stake. . . . (evil grin)