To Cloverjo, I don't think your choice of APKTJS really fits detective C's reference (though it does fit another detective's comment) but there is another group of 4 letters that does. Hedgesparrow has included stuff in the grid to partially support every detective's conclusions, though as far as I can see there is only one murder victim.
I'm also struggling to find a murder weapon. Without some indication of length the whole process becomes a bit of an unsatisfying guessing game. I have two items (one obscure) that could have been conceivably used, depending on their size. If, as some have suggested, the answer is obscure, then I'm not sure that I want to waste any more time on it. In addition, the ambiguities in the word "touching" open up a minefield, as does the possibility of an encoded weapon (though that would strike me as unfair without any preamble confirmation).