The detective was used to kill/sacrifice the woman.. some witch craft or voodoo magic sort of thing used by the boyfriend's family..he always imagine that woman while having sex and when she attacked him..so he was terrified and killed the woman in that frame of mind..
shareI thought it was because he mistook her for the apparition that attacked him earlier
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Reference: The Shining. The apartment has driven him mad and he kills her ... simple as that. The first 5 days are seen through his perspective ... and we see him go slowly crazy (apparitions, sickness etc.). The last couple of days are seen through her perspective and may be the boy friend was right and she turned out to be some form of sacrifice, though that was never really clear.🐭
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