How do we know that Operation Grainge et al, haven't already done some sort of background checks on the Tranmers, and decided they had no need to question them, or have a case to answer for.
Well we know CT had not been interviewed by any law enforcement agency at the time the PJ put the McCann files in the public domain which I believe was around Sep 2008?
The point being no one should automatically slip off the radar due to age, class etc, etc. Even PF, who was in her 80's at the time, should have been immediately seen as a witness/suspect due to proximity alone. And yet we know she was not even interviewed as a witness until Aug '07. Had CAT not interjected herself, law enforcement would not even have known about the Tranmers until Aug' 07. These were 3 people that were around MM constantly during the week hol. I can see no reason whatsoever why the 3 of them were not seized upon on 3rd May '07?
The Tranmers may simply have fallen off the radar due to operating under a 'cloak of respectability' much the same way many paedophiles do within the church etc.
Even if OG has carried out background checks on the Tranmers how does this exclude them? It might just mean they have previous and have evaded detection or they don't have previous.