Dark Souls Remastered | How to escape the prison cell in Duke's Archives (includes full cutscene)

This was not common sense for me the first time I spawned here.

There's a prison guard leaning up against your cell right near the bonfire you spawn at. You can't lock onto him, but you can strike him with a weapon and then loot the key from him.

The only part of the video I cut was at 0:06, when I went down the cell to kill some Crystal Soldiers, but that's not necessary to escape.