Yes, I agree: you usually trust police instinct , but there can be errors. I recall a case in the past, a little girl abducted and killed, and they were blaming the stepfather, as they said the break-in (supposedly how the abductor had entered via the basement) was staged. In the end, an expert proved it was not, and the stepfather (after serving prison time) was exonorrated when the real killer was found.
Having said that, I can imagine, though, when the Postal Police first spoke to the Carabinieri (they were supposed to have remarked, "This was no burglary! It was staged.") it must have certainly immediately made them look at the 2 who found the scene, with grave suspicion.
And indeed: Kuddos to you for being honest about your doubts (as it is true, Raffaelle's words can be taken either way). I do the same; around in circles, because all I really want is the truth, and not for a particular side to win....