How did Edgar Allan Poe create suspense in his classic horror story, "The Pit and the Pendulum?"

I think that a big part of the suspense in "The Pit and Pendulum" comes from two sources.

The first is the unknown. The reader has no idea why the protagonist has been arrested and sentenced. The opening paragraphs have him in and out of conscious thought all while hallucinating. We don't know who he is or what he has done to deserve punishment. Once he is in his cell, the unknown continues.