Adams could have been arrested at any time if there had been a shred of real evidence against him - he wasn't - and to date there is no indication that any new evidence has come to light.

The is now no evidence except testimony.
We know why there has been none of that before.
How do you know what has come to light?
Perhaps Bell has opened up.
Perhaps the family have identified people and they have talked.
Perhaps others have come forward.