Leaves me with concerns about contamination of evidence. My understanding is evidence is fully documented, photographed in situ, prior to any handling, then it is collected within the bounds of good forensic practice to avoid contamination, then given to forensics, etc. At lease we are aware that this item was discussed (presumably in depth) with the LE as part of the negotiation process, and then handed over, so we can assume that the LE was informed fully of it's history. We can only hope that the private investigator took appropriate steps in procuring this evidence, so the LE may have photographs etc as I outline above.
I just can't help but think of the Jon Benet case where the aunt came into the house (wearing a police jacket) and took various items from around the house for the family, and not all these were recorded! AND that in the JB case a considerable number of extra individuals were invited onto the premises (family friends, minister, etc) who impacted on the premises (which admittedly was a "kidnapping" scene rather than a "murder" scene at that time) – this incident reeks of that to me. The private detective would have left his own imprint on the location, and without a thorough forensic background this may have impacted on the complete value of the evidence (whatever it is). What of course is possible is that this evidence was found at another location, not a place previously considered and searched.