Roose Bolton's murder directly mirrored the way he killed Robb Stark back in season three.
One of the shockers from the second episode — "Home" — was Ramsay Bolton's brutal murder of his father, Roose. When Roose went to embrace his son, Ramsay stabbed him in the side with a dagger. This was exactly the same way that Robb Stark died back in season three.