@trt
They recently re-ran the previous series, which I saw enough fragments of to remind me that one of the conspirators was never brought to book and has, indeed come up, in rank.
I can't properly recall the name of the protected witness, bumped off in that series, but we saw more than one name crossed out on that list and one seemed more familiar than the others.
So this latest series is a continuation of the plot and it was never made clear what the dead protected witness had got themself mixed up in.