I just watch the "Disappeared" episode on this case. It seems clear to me that the accountant did indeed kill the Calverts before killing himself.
What I found interesting was the similarities, in a way, with say, the Kyron Horman case, in that he was the last known person to see the missing persons, he had a period of time unaccounted for, he had stopped at a drug store and gone in two separate times (one time buying latex gloves), had lied about seemingly small things (the cut on his hand, etc.) cell phone issues, and although LE could find no physical or forensic evidence they were preprared to name him as their suspect on the date he killed himself, all within about a week or so period of their disappearance. He also refused to take a polygraph and hired a lawyer early on.
Aloso, LE in Hilton Head made use of every possible agency they could, in their searches, as they did in Portland, for no sinister reason, just to have all of the experience and manpower possible. (Portland has also used every imaginable agency.)
I guess I am wondering why LE in Portand is so hesitant to name Terri Horman as a POI at the very least. I know it does not really "matter" but the difference in various jurisdictions interests me.
I'm sad for John and Liz's family that they will never get to bury their loved , but I think the only mystery is where they were left, once deceased.