Originally posted by Linds:
I think it's the senior police officer (I can't remember his name

) who's in charge of the investigation. I think his motivation is an attraction to Tom King's wealthy widow and indeed her wealth.
He was there when Tom King was finalising the paperwork to hand everything over to Rosemary at their wedding so he knew that if Tom King were to die Rosemary would be very well off, and he has shown an interest in her.
I don't think it's any of the villagers.