How does Stevenson use language in €˜the Carew murder case to create an impression of horrific violence and gothic horror?

In the story's opening
paragraph, the narrator describes one witness's experience of the crime, saying,

A maid servant living alone in a house not far from the river, had
gone up-stairs to bed about eleven. Although a fog rolled over the city in the small hours, the
early part of the night was cloudless, and the lane, which the maids window overlooked, was
brilliantly lit by the full moon. It seems she was romantically given, for she sat down upon her
box, which stood immediately under the window, and fell into a dream of musing. Never (she used
to say, with streaming tears, when she narrated that experience), never had she felt more at
peace with all men or thought more kindly of the world. And as she so sat she became aware of an
aged and beautiful gentleman with white hair, drawing near along the lane; and advancing to meet
him, another and very small gentleman, to whom at first she paid less attention.

Here, we have lots of description, visualmeant to help us to really
see...