The title, "Các Tù Nhân," is Vietnamese for "Prisoners."
The book Hetty gives Beale is the same as she read for her "husband" Branston Kohl in the nursing home; The Red Badge of Courage by Stephen Crane.
During the interview Sam and Callen, the older gentle man says the guy that took the photo was from a ranch in Montana. Jeff Kober is actually from Billings, Montana.