HONGCHEON, South Korea—It is still dark. The chilly air leaks in at the windowsill. There's no clock on the wall. Park Woo-sub assumes he needs to wait a bit longer for breakfast to be served through a slot at the bottom of the door to his solitary cell.

"This is my third time in prison," says the unshaven 58-year-old who looks as if he has had a sleepless night. He is wearing a regulation blue uniform with an ID number on his chest.

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