CM said JM was his best friend but he was not JM's best friend. So we can't refer to CM as JM's best friend. I've seen this done more than a few times in different places.
Common sense is that when a family of four have not been heard for days, their relatives should get worried and go to check on them, rather than assuming they went on vacation. Common sense is that relatives don't delay checking on the missing family until being persistently asked by a business partner and friend. Common sense is that you don't do a house clean-up in your missing relative's house before the LE arrived. All these, for whatever good reasons, have negatively affected the initial investigation, which was crucial. Should common sense have prevailed in these instances, the LE would have likely found a lot of forensic evidence to bring the killers to justice.