Mark was able to gain access to Indonesia's Kerobokan Prison to get an insight into their lives there and speak to them for the first time about the prospect of facing the death penalty.
He also returned in 2011 with Sukumaran's mother to hear of her desperation at the prospect of her son being executed.
Watch the interview with Mark, from Dateline's 30th anniversary special, above and see both stories in full below.
