I think that "and Martin Clunes" is a nod to his star status, even though he doesn't have a leading role.
Am quite excited to see Part 2 tonight -- MC has said this called on his acting chops to the max and didn't see that evident in Part 1.
I am on the same track as you NewPark, as usual
Have deleted the ' Spoiler ' for the enjoyment of others
But I do think this is where MC's talents are going to come to the fore...
I have a theory about the killer - just my fanciful thought. Don't read if you don't want to hear my speculation
I wonder if it might just be Ben. Perhaps he caught his son and the murdered girl doing something at his wife's graveside and stabbed her in a rage. Maybe that's why she said she was sorry? Could be why his son is acting strangely and maybe planted the bloody trainers?