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When the prisoner is brought down from Death Row he steps from the elevator directly into a "holding" room that adjoins the witness room. There are two cells in this "holding" room, two, in case it's a double execution. They're ordinary cells, just like this one, and the prisoner spends his last night there before his execu­tion in the morning, reading, listening to the radio, playing cards with the guards.

Source: capote.wordpress.com
When the prisoner is brought down from Death Row he steps from the elevator directly into a holding room that adjoins the witness room. There are two cells in this holding room, two, in case it's a double execution.