And it is, but hearsay is not evidence for exactly the reason told to you. He said/she said without proof (video/audio) is subject to embellishment and bias. It is up to the police to determine the truth, but they are not going to play the "one up" game. They have to go on evidence which requires proof to give it any weight.
There are so many ways they could have obtained evidence to verify official statements and determine exactly what Eric did for the 5 months he was there without any help from either one of them with tons of legwork, paper trails, and credible witnesses. But you have said LE does have a lot of evidence you cannot discuss which led to their conclusion of foul play. If they have that much evidence, LE should move the case from Missing Persons to Homicide.
You mentioned a private investigator at one point. Is this person still on the case?
The cover photo on his Facebook page with the fake thumbnail burning his photo should be investigated as possible evidence, imo. It is a glaring reference to him going missing. With a search warrant, they could find when it was added, information on the origin of the photo, and other valuable data. Without a doubt, there is other pertinent information on his Facebook page only accessible with a warrant. If a person put up a note that said, "I am here and Eric is gone"...wouldn't they jump all over it? It is the message I get from that photo.
His Facebook page is a goldmine of information and possible evidence, imo. Getting his password wouldn't be enough because you need a warrant and a professional in computer forensics in order for evidence found to be used in court I believe. Granted, LE cannot do a fishing expedition on his page. They must have probable cause to get a warrant. (I wish we could have a legal professional weigh in on this. Hmmm...I know we have a couple on WS. Can someone give me a heads up on our legal eagles here?)