I think we have all seen or read about 'hearing voices' and 'the voices told me to' or 'the devil made me do it'. This was always something of a 'wtf' for me and I don't know how much of this is media drama and how much is based in fact.
But let me back up a bit. Has anyone else ever experienced this: you spend some time doing something very visually repetative (say, playing Tetris) and then can still see it when you close your eyes? I know I have (Tetris is just the one I remember best). I could 'see' the basic layout of the game and there was the ... suggestion? essence? impression? (not sure what word works best here) of motion but no details. I couldn't see individual blocks or anything like that. It was kind of like the afterimage of the game (motion and all) imprinted on my retinas. I thought the phenomenon was rather facinating.
But it seems to work with sound, too. If I listen for long to something with an even tone (say an audiobook or a lecture) sometimes I can still 'hear' a voice talking. There's no words, no real sounds at all, just the impression of a voice: the inflection, the tonal changes, the rhythms - in fact everthing EXCEPT actual word sounds (how that works, I couldn't tell you. And believe me, I have tried to figure that out). I can even recognize the 'speaker' sometimes.
If this happened often (it doesn't) or to someone more unstable than I am (at least, than I think I am) I can see how someone might try to force some sense into it. Why this hypothetical person might decide they were being told to kill someone, though, is still beyond me. On the other hand, this might happen rather more than anyone knows about, but MOST people don't get noticed because, frankly, they don't end up killing anyone (or even trying to).
I dunno. But I find it just as facinating as the visual version.